Sounds like everyone is doing everything right. We are all here on earth to live our own experiences and learn our own lessons.
You already have your answer: The children love their mother, the mother loves her children.
I know it can break your heart sometimes, but we’ve got to live and let live.
I lean towards Raycpa and Momtothree's advice - our friend and we will stay connected to the mother, letting her know that anytime she needs help, we are all there for her.
The support network is a good idea. Prayer with the mom and being able to watch the children is a bit hard due to the distances, but we'll offer to take them for the "holidays" (that's what we told the little girl now that she's just with us for her holidays and will go back to mom as she was scared that her mother left her).