I have not seen lots of newborns.  I have seen lots of small children.  I have seen more than one 2 year old careening down a slope and knocking into another child.  Usually it is accidental, or an impulse of fun or wanting to say hello.  One child I saw deliberately lining up the child it felt entirely calculated - if I run now as hard as I can I can head-butt him hard enough to hurt before anyone can stop me.

Then I've seen a 5 year old on a skateboard messing around on his skateboard in front of the kiosk, they were waiting for their parents to come and pick them up and the girl was a bit little to be left alone so I was keeping an eye on them and I saw him quite deliberately drive into his little sister's head where she lay on the ground - but you know it didn't feel malicious in intent.  More investigative - what will happen if I do this (she cried).  He didn't take pleasure from hurting her, he was just bored.

I've seen a ten month old take pleasure from hurting his father, ouch.

Some people will laugh at the sight of someone slipping on a banana peel but there might be another who has a light in their eye, that small smile of satisfaction because they were the one who planted the banana peel.