I use the pre-quilted backing for mine, which has a light loft sewn in already. I do quilt the back and the top together because I am sewing for kids and animals, and they wear longer. I always put a good strong binding on mine too for wear purposes.
Since my sister got sick I have gone to mostly "strip quilts." I just made 6 the last couple days with red, white and blue stripes. Kids love loud colors so try to keep them interesting.
Also make lap quilt size for an adult which is a good snuggle buddy for the kids. They lay on the floor and watch TV, play with clay, and most have names for their quilts, so they are "friends" too.