It sucks that this happened, and I can't really speak from experience concerning chickens, as I haven't even began my own flock yet, but...
The only age of the child you mentioned is a year and a half. You say you explained to the kids how they cannot go in there, but a year and a half year old will not grasp that concept. Your sister also should not have an unsupervised year-and-a-half year old.
That being said, I understand how with four children in a different place than she is used to raising them, she could get flustered and there could be mistakes... I love children, and have raised my three siblings due to reasons I will not go into. I am in a lot of four children, and this is my opinion:
Why in the world does someone need four children?!
Two, max. Replacing you and your spouse.
Then again, I plan on adopting ONE child, so whatever.
I think everyone's a bit at fault here. You seem unwilling to admit you could be wrong, and I'm sure it is not impossible for you to somehow lock the door. I can child-proof a door with a nail and a piece of board. Nail to wall above door loose enough that you have to be able to reach to swing the wood out of the way to open it. If it's a inward-way door, you tie a rope the doorknob and a nail. It's not perfect, but at the very least, it allows more time for the kid to be caught or that they give up. Your sister seems like a bit of a twit in this whole matter as well, and kids... Well they're not being punished when perhaps they should be reprimanded, but can we really blame kids for being exactly where you don't want them?
I'm offensive, oh dear. I just think everyone could have helped avoid this, and as such, everyone needs to learn from this mistake to prevent it happening again.
