you aren't being heartless. it's natural to want a thank you.
however, put yourself in the family's shoes. if you were living through the same circumstances can you honestly say you absolutely, positively wouldn't let sending a thanks slip your mind? isn't it possible that everytime his mother sees him cuddling in your quilt she reminds herself she needs to say it? or feels a twinge of guilt because the complications of their present life keep getting in the way?
give the family a second gift. it won't cost you a thing.
let them off the hook. you'll feel better for it. ;-)