I have two boys, the oldest will be four in two weeks and the baby is 19 months. My older son has been getting very agressive with the baby, pushing him down, hitting, kicking, pulling his hair, etc. I put him in time out or in bed, and I have tried to explain to him that this behavior is unacceptable. I am afraid that he is really going to hurt his little brother or even that the baby will pick up the bad habits of hitting/pushing/pulling hair/etc. I have no idea what else to try...does anyone have any ideas?

I do want to say that I have no children of my own, but I have been a nanny/in child care for a long time. If you are not one for any kind of physical discipline, and many are not (and you can't be with other people's children) then my answer would be longer time outs. If the time out doesn't get the message across, start increasing it in small increments. Also, where is the time out taking place? It is best (in my opinion) to have a chair in a hallway, where you can make sure that it's not being enjoyed.

Hope this helped. Good luck!

Since he is 3, almost 4, I usually do 4 minute time outs. But when it comes to being mean to his brother, I have been doubling it. The time out is either in the kitchen on the time out mat or he has to stay on his bed (no toys in there, they have a playroom). But he gets back up from time out and starts it all again. I don't spank, or any physical discipline, I don't want to either. I have showed him the scratches and marks where he has hurt the baby and he thinks it is funny. He doesn't treat any other kids like this, I don't understand it.

Could be jealousy. My niece acted like that when my nephew was little. The two of them were about the same age as your kids. She was just affraid that he was getting more attention than her, and a lot of the time he was.

its a jealousy thing..
maybe you could encourage him by having just you and him time when the little one is napping.or let him help you with tasks around the house.i think he is feeling a wee bit insecure right now and this is one way to get your attention,negative or not.

u have to make time for u and him!! when all of u are together, you must involve him, whatever it may be....let him be a teacher...children learn from childre...encourage play between both...

First off the developemental levels between a baby and a 4yr old should be as obviously different to you as would be the difference between you and someone four times your age. This wasn't going to work from the start so don't beat yourself up just because your older child doesn't perform like on 7th Heaven. You trying to make the impossible possible? Ok live and learn. No serious harm. Don't get on a guilt trip.
Don't make this into something it isn't. Your preschooler loves the baby and the baby loves him they are just mismatched. GIven time the will catch up but a four year age span it is not likely they are going to ever be the best of playmates for many years probably not until some time in their early thirties. Sorry that is the breaks.
However breath a sigh of relief and read on. A certain amount of chest pounding and agressive behavior, commonly known as rough houseing at 4 yrs is actually a normal developemental marker so relax.
He just doesn't understand and quite probably has not mastered his new growth spurt and strength but he is testing it on everyone and everything. He might try for easy and only get ouch. He has probably plowed into you and I suspect put a few bumps and brusies on your shins you have already forgotten about. If he hasn't slung a baseball and plastered you in the face it is coming. Eye and hand coordination ebbs and flows with each streach and fill as your kid grows. Also Four year olds freqeuntly break toys, even beloved toys and injure pets, or are injured by pets reacting, as your preschooler tests and practices their new found play/fighting skills. It doesn't mean he is a candidate for the next Charlie Manson. But it is also not a good time to add a pet companion. If you have and older pet around you might want to segreagate them also.
He also doesn't have the brain developement or experience to understand the the baby's vunerability any more than he understands you are much stronger. It is going to probably be a long process 6 months to a year teaching him easy, gentle, and cause and effect. Obviously you don't over power him so the natural consequences are not teaching him limits as quickly. Eventually he will tangle with a playmate that will overpower him and he will develope some sense of the pecking order and it's conseqences. Probably a nasty bite, a black eye, bloody nose, or the wind knocked out of him. It is not likely that a baby could return behavior but another smaller preschooler with older siblings might. He will cry and you will be tempted to comfort but a calm "don't start something you can't finish" remark and walk away will be much more effective. You can give him a sense of dominance by pinning him face down on the floor with just your upper body but be prepared for a scratching,biting, head butting fight. If it is the first time you have truely dominated your preschooler versus the wimpy go set on a mat punishment it will be a shock and a draining experience for you both. If any one interceeds it will only last longer. If you are going to give up then don't even start because you will have just made a four year old King of the Jungle. I realize there are many who will say oh know I cant do that but sooner or later your child will be dominated and and hopefully it won't be by someone who will actually hurt him.
What is essential to realize preschoolers have no concept of permenent injury or death. The baby quits crying he thinks it is over. Preschoolers have actually killed siblings and not known it. You can show him the marks later but he doesn't remember doing it past a few hours. He just can not connect the responsibility his actions. Especially things like bruises that don't show up immedidately. Or stitches or casts that appear hours after xrays are taken. Sometimes they do associate bite marks or scratches but their impulse control is still so under developed it is just not going to connect.
A four year old may laugh when disciplened because he is experimenting with your response to his reactions and trying to go back to playing. They really don't enjoy inflicting pain but they do enjoy the attention you are giving them. Especially if it takes away from you paying attention to the baby.
The reality is you are going to have to segregate baby and preschooler as playmates. Not every second of every day but the majority of the time. Do this as quietly and calmly as possible. Don't tell your child it is because they were bad because all they are going to get out of it at four is you think they are bad.
The GOOD NEWS is All chldren have times where they are calmer and in better control of themselves than others. Look for the optimum and short times your Preschooler can share with the baby and keep the play at a mellow level. Babys swing toys ad throw things so try to avoid letting the baby do behaviors you do not want reciprocated. Praise and reward the Preschoolers positive behavior and when your he seems to be looseing track of being gentle withdraw the baby and your attention but do not berate him or punish him or you will feed the jealousy and break down the bonding with this boreing baby playmate. It sounds cruel but really all your Preschooler knows is smack baby like a drum, he makes noise. later they learn Mom comes running, and I get attention. inadvertently you are re-enforceing the behaviour you want to stop. Sadly with divided attention of a new baby negative attention is better than no attention.
One thing I would recommend if you see that your four year old is getting more cranky is see if he is actually over tired. As they get older the tell tale signs may change some. Is he sighing more. Is he clinging to toys. Is he more territorial. He may not suck his thumb or rub his eyes because he might have caught on hiding the old signals is wise but a littel observation and experiementing you will still read his more mature body language. It might be other factors but here are some common ones. Is the baby waking him up at night? Have you deleted a nap time too soon? Is the preschooler getting up earlier to go somewhere? Are you bathing your preschooler later or letting him other wise be stimilated (TV while you play with the baby) so he doesn't get as much pre-bed time rest as he used to? Have you added colored multivitamins because he is on a typical four year old food jag? Not as a punishment try adding in 30 minutes sleep for at least five days and see if things improve.
Last but not least check around and see if your Preschooler is getting anything that might be giving him an allergic reaction and negative behavior. Now that he is off the bottle and sippy cup are you allowing more soda or chocolate? He has more teeth what new foods? Is he wallowing in the dusty grass more? Have you added a pet? Have you graduated to more highly perfumed mainstream big boy soaps. Have you changed his bed? Are his sleep toys getting old and grubbier than maybe you noticed? Is he watching much more aggressive TV programs? A new baby is undoubtably not the only new thing in life but it is the big one so it tends to get all the blame when maybe it really is several things. Good luck figureing it out.

let him help take care of the lil one with small tasks. (i.e. giving you the diaper, bringing a snack, ect.)compare their height and hands and feet so your oldest can see just how much smaller the youngest is in comparrison. and maybe take some time a few times a week for just the two of you. let him get involved with some smaller tasks at home. it helps to see the differences between him and his lil brother and the "chores" help him feel involved and important. it works for my 4 year old who has 2 younger sisters, and is helping my oldest daughter to be gentle with my newborn.

I wish I had some helpful hints. Mine are 6 and 2.5 (both boys). I didn't have this problem. Mine OPP. of yours. LOL My little one won't leave his brother alone sometimes.

I do think you can ask the big brother if he wants to help with things are around the house that involve little brother. My son LOVED doing this for his little "bubba" as he called him.

I think the original poster is on the right track. When I was younger my older sister would like to light matches and then hold them to my skin. My dad saw this then took a match and lit it then put it up to her skin. She then went ouch like I did when she would put the match up to my skin.