After shopping for fabric (which, incidentally, I think should be an Olympic sport ;) ), I found two combinations that will work wonderfully--not too grown-up but not babyish.
Fun, right? I'll line them both with white cotton that has been laminated (iron-on laminate) so that spills won't soak through onto Lil' Miss, but have it on the bottom layer so that drips just don't run down the front--a great suggestion from ColorKitten over at PatternReview (thank you!).
However, I did need to rethink my pattern layout a bit with this fabric. I didn't want stains to show up a lot, so the lighter fabrics will be on the lower part and I'll need to extend the darker fabrics for more coverage. Here are my illustrations of the aprons I have planned.
I kind of merged the idea of a smock apron with some of the Japanese styles that have been becoming so popular in the sewing world these days. I think they represent a good balance of style and function. Now to work up the patterns and test them.