1. "Thank you for taking care of my children these days. I believe he/she has a good life in your home and is well taken care of. I feel very relieved. "
2. "I know my children are doing well in your home, and I thank you very much. Does he/she need anything? I hope I can do more for him/her. "
I am very grateful to you for taking care of my children while I am away. I know he/she is happy in your home, but please tell me what I can do for him/her. "
4. "I want to ask, the child's aunt, what can I do for you?" If there is anything I can do, please let me know. "
These words express gratitude and concern, and also express your wishes. I hope the child's aunt knows that you are very grateful for her help and are willing to do your best to repay her kindness.