Just because we are discussing this on our local list, I thought I would mention it here...
I've never struggled with a toddler/pre-schooler hitting a baby...but I do have a toddler who likes to push younger babies over sometimes. Not all the time, but more than once- and that is enough.
If I hadn't had Tombliboo, I probably woudl have supposed there was something odd about the family...now I can see there is very little I can do about this fact...except try to prevent it.
Since I don't really know *why* Tombliboo likes to push people over (I have a wee suspicion that newly-walking babies look a bit like skittles, and possibly he is thinking it would be fun to watch the baby topple?) I just have to keep close lest the desire strike.
I have noticed that preceding any episode, there is nearly always a bit of a cry for help...this is usually in the form of actually saying, "I want to go home."
This is him letting me know he has had enough, there is too much stimulation for his brain, or he is tired, or hungry, or just wants to be in his own space (where people love him best of all).
If I am too slow, and Tombliboo does hurt someone...I apologise to the parent, and then get down at eye-level with the child who is hurt, and apologise on Tombliboo's behalf.
By this time Tombliboo is probably bawling- he knows something is not right, I'm not certain really if he has gleaned that he has caused it.
After I have done as much as I can (I think?), I snuggle Tombliboo and tell him, "You hurt the baby- you made him cry. He didn't like being pushed over, and now he is sad- I hope he feels better soon." I might invite him to come and see if the baby is OK. I might suggest saying "sorry", but I don't push that- there is o point. Children, like adults, say "sorry" when they feel sorry.
Sometimes people feel so terrible about what they have done, but so confused or even angry about the consequences, they are simply not ready to say "sorry" right away.
Tombliboo, who is not a bully, has been pushed and shoved a few times himself. It is so uncomfortable watching a mother try to force a child to say "sorry". It's worse when they don't do anything, of course, but I can tell when a child is genuinely sorry, and it has nothing to do with saying a word.
Anyway, I'm rambling. This link is wonderful for ideas about children hurting other children. It's aimed primarily at those with siblings, but it is really about any child relating to any other.