SIL is moving back in with MIL and FIL due to her ending her engagement with the fiance she was living with. She has this dog, I don't know what breed but it is a smaller dog, probably 10-15 lbs and very hyperactive.
In the past, when we, me, DH and our children, 4 year old DD and twin 20 month old boys visit the dog is always a problem. They will lock the dog in the laundry room for a while but then SIL gets upset about her "baby" crying and lets her out when no one is looking and refuses to put her back. When this happens, she will jump up on my kids. While she is not a big dog, my kids are young and she can easily knock the little ones down. She also scratches and nips. So at that point, we have to leave for the safety of the kids. MIL and FIL don't see the "big deal" about the dog "playing" with the kids.
Well MIL has asked to have the kids on Thursday mornings, just to have time to herself with the kids. It has worked out well so far, they enjoy it and truth be told, it is nice to have the morning to myself. Well when I found that SIL was moving in, I told MIL that if she moves the dog in, the Thursday mornings will stop because I don't trust that they will keep the dog locked up when the kids are there since they don't even keep her locked up when we are there. Plus, SIL refuses to pick up after her dog outside and so the kids can't play outside because I don't want them stepping in dog crap (this has happened before).
MIL said she just can't tell SIL not to bring her dog and she feels bad telling her to keep her locked up, even while we are there, because SIL can't have children so this dog is her baby.
Maybe I am wrong but it feels like MIL is choosing a dog over her grandchildren. It would be one thing if I could trust them to lock the dog up or if the dog was well behaved but that's just not the case. I feel like telling MIL, the dog is not SIL's kid, it's a dog.