5 years old isn't too young to start, she just needs to do things that are at her level of ability. When Bri and I did the first quilt I had her guiding fabric while I controlled the pedal. We did the stitching around one of the birdhouses today and I guided the fabric while she did the pedal. Once they get used to each part of it they can start using them together.
I am teaching her about contrast and trying to gently guide her to making good fabric choices. I don't want to interfere in letting her choose her own colors and I don't say anything unless I am pointing out something like the plaid roof fabric is the exact color of the house and showed her from several feet away that you can't see the roof. She did another one and commented herself that you can't really see the round brown hole against the brown house. :-)