According to the article the 3 y/o left the gate open, I think that we all realize that there's enough blame to go around, but you are going to have to really protect that kid, you can't have him growing up with some guilt trip when, in reality, it was most likely due to lack of supervision on the part of some adult.
I've personally responded to several kids who ahve drowned and all I can say is that it really truly sucks, older people at least have had a chance at life but I never get over kids (the last died at birth in an apartment) and despite trying to do all we could there really was no hope for the little girl.
It's just hard on everyone, good luck with it, but I too believe there's a reason for it.