im making my granddaughter a flannel quilt can i use cotton fabric for the binding?

Absolutely! There's no rules. I've done it before.

Definately use cotton. The flannel will be a little bulky and because of its nap will probably not wear as well as a cotton binding. I do it all the time and there is no problem that I can think of.

Your quilt, your decision! :D:D:D

If it's a rag quilt, you can also rag the edges so you don't have to have any binding.

Of course! Hope you will share pictures!