This sounds odd but where do the parents live? If they are in a warmer climate you might just leave out batting. There is something called a summer quilt. In places like the deep south and the tropics quilts don't have any batting.
If they live in an area that has definate seasons then batting would be necessary. With a flannel back I would use the thinnest poly batting I could find. It will give the quilt loft without adding weight.