I work with our local chapter of Project Linus, and the only suggestion I would make (cautiously), is that if you are going to make bigger ones, don't use baby fabrics – save them for baby-sized quilts. I've seen blankets made that were pretty big with pacifiers and such, and they really aren't all that suitable for older kids.
Also, the blankets don't have to be big enough to use on a bed; I know I get caught up in thinking that, but really, the blankets are for cuddling so they don't have to be huge. So I guess my point is, don't worry so much about the size, because there will be a child the right size waiting for it.