Grandparents Raising Children Support Group
This community is dedicated to grandparents who are the primary caregivers of their grandchildren. In cases where the parents are not willing or able to provide adequate care for their children, grandparents may take on the role of primary caregivers. Join the support group to find support, share your experience, and get advice from other members.
I would make it very clear to the school that NOBODY is to see the children except you, and whoever else you've authorized. Taking them is a very real possibility, IMHO.
The only benign reason I can think of is that he needs to know the name of the school in order to pretend that he's involved in their lives. Perhaps it's on some paperwork he's filling out. But I would assume that there's a more nefarious reason...
That would scare me half to death.