Here are a few things that have worked wiith some young adults in shows I've done (just like grown-ups, you have to adjust to the person) - and if you know any Jr Hi School/ Middle School teachers, their tricks really help too - test a couple out, see how they work with your collection of kids and go from there -
- As SMRose said, telling them WHY can help - esp when it ties to cues and existing lights - if they are brought into the circle of planning it can help them be on the team rather than just showing up and not understanding how everything relates - the domino effect of any one change (ah, the butterfly analogy)
- Deputize the person who abuses the most and make them like a de facto AD - sort of dance captain equivalent, to keep an eye on the show and keep it tuned to the director's vision
- If you can show an (bad) example in the adult cast, it helps explain "different" doesn't always mean "better"
- Praise the performance every time it does what the director intended with words like "wow, it was so simple and clear tonite, you really touched me" or "the audience really loved it when you...." - as in, specifically manipulative reinforcing specific original blocking/intentions etc
- Depending on their age and experience, you can give rewards, from gold stars to something inexpensive but fun to win based on earning a certain number of performances without changes (something you can afford easily or purchase w petty cash that a person that age would love to win) - awards can be given weekly or monthly, and (in a show like Annie with so very many little girls) even divided into teams, so each team polices themselves since if one person strays, all lose. ** Be careful since this can work like gangbusters or can have repercussions if there is one person determined do what she wants regardless - you really have to know your cast to do teams.
I am sure you will get a slew more great ideas, but I have found these to work well - at least so far- (kids these days...<g>)