I have a six year old, although this is not homework I do extra tuition with her on maths because she wants to. She bugs me to set her maths questions for her, because she enjoys them. I set them because she enjoys the challenge. I think as long as children enjoy it and don't see it as a choir then its ok. If they resent it though, then that's going damage their love for learning. They need to enjoy learning for learnings sake. Homework needs to be optional, my school also offer alternative pieces of work so the kids can pick one they will enjoy doing the most.