when I do kids I love to do 6 inch square quilts, I've got a die cutter die that cuts the perfect squares that finish at 6 inches and then I can just go nuts with fun fabric with themes they like (cats, dinosaurs, fairies, space, science, etc)
Sometimes I'll do a panel with squares around the sides but I often find that panels aren't printed very well which is frustrating BUT the kids certainly don't mind.