My first vote would be to tie them. Easter is almost here & that will take long enough. But besides the benefit of it being quick, tying will allow the fleece to maintain its fuzziness. You certainly could do a wide cross hatch (I'd suggest 4", but a minimum of 2" spacing) but that would give you puffy squares rather than a pretty consistently smooth fuzzy backing. You could tie with either yarn or floss. Depending on your color scheme & the age of the children, I've seen people use variegated yarn/floss and it looks really cool. Wish I'd taken a picture, but I have a college friend who got a denim front/flannel backed quilt (as did her 7 siblings) that was tied with rainbow variegated yarn and it was so cool!