Things like this happen, be happy that everyone else is OK. I am really sorry about the chick but it didn't suffer and is in a better place now.
Please don't get depressed over this, I got depressed when my cat died (was hit by a car, I forgot to bring her back inside) and I don't want you to feel the way I did. It wasn't your fault and it wasn't your son's fault. It was nature, and everything goes on.
As a Mom of a 3 year old boy and 5 year old girl, I understand your frustration.
But believe me, there was not an ounce of harm in that child's mind. Just the fact that he was bathing them shows that his intent was to 'tend' to them.
How sweet of him to think they needed a bath.
It was an accident. An accident that could happen to any one of us Mom's.
Go wrap him up in your arms and give him a great big hug. It will make you feel so much better.
Please don't get depressed over this, I got depressed when my cat died (was hit by a car, I forgot to bring her back inside) and I don't want you to feel the way I did. It wasn't your fault and it wasn't your son's fault. It was nature, and everything goes on. 
