Children's hospitals, CPS, domestic violence shelters, homes for unwed mother's, Salvation Army, and probably a dozen more places that can use them.
Maybe contact your local agencies and see if they know where the biggest need is in your area? There is a number like 611 or something like that, and they have lists of groups that can use donations.
Then like Holice mentioned, contact them individually to see what sizes are needed. Or for any restrictions...
Some hospitals need smaller isolette covers and preemie quilts, others can use any up to toddler sized.
You may want to also avoid Holiday fabrics, not everyone celebrates the same ones...
Keep them simple and well quilted. If they are going to hospitalized children, loose binding can catch on IV lines and other medical equipment.
They also usually request that you NOT use any kind of invisible thread on them.
Avoid loose, 3D type of appliques too. Everything should be completely stitched down, no loose sides.
Heavy quilting helps them to hold up to hospital washers and dryers.
Fleece may not stay soft from the heat of their dryers either, they tend to singe them and make them rougher feeling.