Do you mean junior size (5,7,9,etc.?) or learn to sew patterns? I don't think there's been a junior size pattern for years, maybe since the 70s when they changed the sizes. A junior size is usually shorter waisted, with a higher bust dart and, if I remember correctly, a slightly smaller bust size than a misses pattern compared to the hip. You can always shorten the back waist length.
How old are the 4H girls who are learning to sew? Has anyone measured them? I'm asking because a lot of the young girls these days are quite a bit taller and heavier than their mothers and grandmothers, so might fit a misses pattern just fine. The size charts are on the sewing pattern company sites. This is the one for McCalls, Vogue and Butterick:http://www.mccall.com/
If it's learn to sew patterns, perhaps someone else has a suggestion. I'm partial to Vogue patterns as the instructions are usually more complete and precise than those of the standard McCalls and Simplicity patterns which sometimes let you guess what you're supposed to do next. There are lots of independent pattern companies, too, so someone else might be able to steer you to one which has simple to use patterns suitable for beginners.