My husband says, "As big as your stash allows" LOL! Does he know quilters or what? He works at one here in AZ and I have worked for one in the past. The last batch I made were just big enough to cover the lap and legs when sitting in a chair or wheelchair. I used 6-12 inch finished blocks with large border and the larger blocks I didn't put any border around. [ATTACH=CONFIG]306854[/ATTACH][ATTACH=CONFIG]306856[/ATTACH][ATTACH=CONFIG]306855[/ATTACH]
I also put flannel on the back for warmth. Just make sure that they can stand up to multiple washing. It is just like a baby blanket, they get wet and pooped on and need a bath frequently
.... I am sure they would be happy with any size quilt you want to make. They always love to be able to give a little extra 'love' where it is needed.