Definitely use muslin on the back and send it off as a charity quilt. Just because you don't like the final outcome doesn't mean you didn't put a lot of hard work and time into making it. It deserves a good home even if that home isn't where it was originally intended to go. Children aren't anywhere near the critics we adults are. I'm certain some child will have a lot of joy brought to them when they receive this.
Quilt it and send it on it's way! :)