Please, DON'T TOUCH

Me??---I would disassemble the system,place it in a closet,speaker drivers facing a wall---this way you don't have to repeat the "don't touch".

I had a babysitter snap the cantilever off of my cartridge while playing LPs for the kids. It's a difficult situation. Our home was more or less 'child-proof' where the knobs, and TT were well off the floor.

Would it work to just unplug some of the gear, say the amp/pre-amp. If you have a TT that is within reach of little fingers, you would be better off to put it away. No parent is going to let their child ruin something, but why take a chance with a whoops? Make sure speakers have grill cloth on, and are solidly placed. It hard with stand mounted speakers. Kids could knock them off the stand.

Use whatever precaution is available, just asking might not be enough, and there is no sense loosing a friendship over a week without the system. Good luck.

Its simple tell the kids parents that the stereo is off limits

The key is to avoid to tell them DON'T TOUCH. No matter what way you mention it they would feel uneasy to stay at your place.
Disassemble the whole system and put them in the corner with drap cover it.

Put the kid up for SALE on Audiogon !!!!