Having had the misfortune of A1ing several different productions of Annie and other shows with body-miced 11-14 year olds, I have a fair amount of experience with this. If they wear a bra or leotard there is pretty much no reason that they couldn't put the pack there but I offer this with a couple of caveats:
1. Don't ask them to put the pack anywhere. Show them the pack and offer them a few possible locations (leotard, bra strap, ace wrap on thigh,
etc) and then let them choose which option they like most. Making it a question versus a request is important.
2. You may find that the bra strap doesn't work with middle school girls if the packs are on the heavy side since they are typically insufficiently developed to stop the pack from sliding down their back and pulling the whole bra uncomfortably out of place.
3. You can't be the one who places the pack. In most cases it is 100% fine for you to place the
element and do any other shoulders-up work that needs to be done as long as you are careful and gentle about it but it is highly unlikely that you would be allowed to put the packs under their clothes nor should you even if it is technically allowed unless you are a girl placing the pack on a girl. I have seen one male A2 get in a lot of trouble for "inappropriately touching" a middle-school aged female cast member on one production. No one involved in the
theatre actually thought he had done anything wrong and in the end the exonerating truth was coaxed out of the involved minor but the risk of something innocuous or accidental making a child uncomfortable and causing you major life changing headaches or legal troubles is way to high. I don't A1 anymore but when I did I would frequently place packs for female cast members who asked for assistance with that but I would never even consider doing that were they not 18+. Have a same-gender teacher or parent do it after you show them how.
4. It is really important with younger cast members to talk them through what you are doing. With an older cast member with whom I have a report, I might rip off a piece of transpore without prior warning and that is no problem. With younger cast members it is really critical that you tell them exactly what you are going to do and then do it. This doesn't just apply to the first time you mic them but every time until the run is well into the double digit performance numbers and you have developed a relationship and understanding with the cast.
