Please, DON'T TOUCH

If you have pets expect the kid to chase them at full tilt around the room with the usual consequences. Without pets watch for the peanut butter sandwich in the CD drawer routine. It's hilarious!

Simplest solution is a straight-jacket for the kids and if the parents complain, crank up the volume till you can't hear 'em. Truthfully a six year old should understand the word "NO" but in a new envirment anything is possible. Unless your freinds want to hear your system and share your passion I would dis-assemble it and lock it away.

at 6 kids are like magnets for disaster. put your system away in a safe place. even a well behaved child might have an accident.

I would recommend a combination of what has already been said. First, unplug the power from everything. Second, turn the speakers to face against a wall, plugging any ports, and draping cloth over them. Third, disconnect any turntable and hide it on an upper shelf in a closet. Fourth, drape cloth over remaining components. Fifth, tell the parents that your rig is out of service and in a fragile state and you would appreciate it if no one touches it, urging them to communicate this to the child. Good luck.

this is a hard thing to do! Having 2 boys less than 6 yrs old that are curious kittens, I can empathize w/ your situation. Little boys love buttons to push! :-) The more, the merrier for them!

well, if you have speaker grills, then deploy for sure. They can protect the drivers unless the child does something drastic. You can also mark the speaker position on the carpet w/ tape. Then move the speaker against the wall w/ the drivers pointing into the wall i.e. the child can only play w/ the speaker binding posts. This ain't so bad.
Another thing you can do is, unplug the equipment so that it does not respond to the button push. The little fingers want to push the buttons & see the equipment light up. when it doesn't (it's unplugged) their enthusiasm wanes rapidly & they leave that equipment alone. Also, know that buttons on stereo equipment are designed for many pushes before it actually fails.
3rdly, if you have spare bedsheets, thrown them over the gear (much like you would over furniture when you paint the walls).
FWIW.