I need advice plzzzz!!!

Kendra • Happy Mother of 4 and trying to do the best that I can
My brother is dating a girl that I have been friends with for a while. I have been keeping her 3 children out of the kindness of my heart. Its starting to get on my nerves and I want out. Her kids are constantly breaking things and she doesnt offer to pay. Just recently two of her kids broke one of my daughters crib. How do I tell her I dont want to watch her kids anymore?