I taught a class at church this last year for 9-14 year olds...we even had a couple younger. We made a big hobo bag...they did it all just fine...except it required fleece stuffed handles...that were a big a struggle to do...but other than that they did it.
I saw on Nancy's Notions website 18" doll clothes that are preprinted on fabric that only have a few straight seems to sew...I think this would be good for a beginner.