I found some great patterns and other helpful information on this website:
Clothing does not have to be exactly period appropriate, but we want to have the same look.
Aprons are not required for our young women for trek, but they come in very handy and help to keep skirts clean.
Here's the direct link to the apron pattern
Here's a link to a sunbonnet pattern
If you would like to borrow a pattern for a sunbonnet (more traditional than the pattern above) and skirt, contact Sister Dupaix (email@example.com). There are four of these patterns circulating through the ward.