It he did kick the ball, as said, it could have done a lot of damage and he has enough control over it that really it wouldn't have been an accident.
The baby had a minor head injury and concussion, that's bad enough.
She was sitting still and there is a 'no ball games' rule, so he is at fault.
The family are more than able to go somewhere were they can play football, so there isn't an excuse.
If the baby had of had a minor head injury from a dog, this thread would be completely different.
Babies in prams shouldn't have head injuries inflicted on them.