For wheelchair lapquilts I would not use a batting. Either just have the flannel backing or, if you want a bit of extra thickness, use a flannel for batting and backing. It would be easier for the kids and quite a bit cheaper. Might I suggest you do a 'self-binding'? Keep the backing 1" bigger and double fold it over to the front and then topstitch (I like to use a decorative stitch) to hold the binding down. This would be easy for the kids and it eliminates the possibility of binding coming loose. As wheelchair quilts or nursing home quilts, they will get some hard use and lots of laundering.