How do I get my 3.5 year old son to quit hitting, pushing, and kicking my eight-month-old son? He tries to do it without getting caught. When I ask him why he does it, he first says he didn't do it and then he says because it is funny. Thankfully, my eight-month-old has not been hurt, but I am worried about letting them play together. My 3.5 year old plays well with kids his own age in preschool.
Sibling rivalry is alive and well in most families with young children. So don't be surprised about your older son's actions -- it's pretty typical and expected. Just think about how he feels -- he had you all to himself, and now he must share most every waking moment with a noisy, demanding interloper. And he's too young for us to expect he'll be "mature" enough to accept his baby brother gracefully -- OR that he'll be able to "explain" his aggressive behavior to you. Those are all very advanced emotional processes that will take years to develop -- with your help, patience, and understanding.
In the meantime, it's up to us as parents to protect the younger child while the older child is around. Be matter-of-fact and calm about it, and don't make your older child feel ashamed for his aggressive desires -- but DO let him know you can't allow him to hurt his baby brother. Heap praise on your older boy when he plays nicely with the baby -- even if it's only for a few moments -- and point out how much the baby looks up to his big brother. Also, the more you keep your older son active and entertained with age-appropriate peers and activities, the happier everyone will be!