For me Charity means scrappy, simple, fast, yet fun and well made! Some of my favorites are disapearing nine patch, strip quilts, and the Amy Butler pattern, Amy's Lotus Brick Path Quilt (can be found for free on her website) which (for a child) looks super cute with a simple silhouette of anything, a cat, dog, car, truck, animal, plain, train, or whatever raw edge appliqued in the lower corner.
All of these can be made with a number of fun scraps in ANY size, these type of quilts are easy to make whatever size whether you are sewing for a preemie or a 6 foot teenager!
And my favorite part about these quilt, they do not take ANY type of thought process! lol
as far as what size to make, it really depends who you are donating to, if you are donating to a NICU they only need to be about 12-13 inch square, if you are making for CPS/foster kids think anything from newborn to 18 years, if you are donating to wounded soldiers, think adult/lap quilts that can be used while in a wheelchair or just hanging out in a military hospital away from home. If you are donating to a nursing home again think something that could cover ones legs while in a wheelchair.