How on earth did ....well never mind.  I hope it goes without saying that you first disarm this thing either by unplugging it, or by removing the battery.  If it is a wind-up toy, you lose, cut it free while being careful not to catch yet more hair in the process.

After the item is disarmed and no longer doing whatever it is that it does, you will need the cooperation of the victim so stop laughing at them.  At least for today.

Examine the item to see if there is a way you can disassemble at least part of it to get at the hair.  Then, using a rat tail comb or similar long pointy thing, begin to unravel the hair from the end of the hair working inward, not at the scalp end of the hair.  You may need a nail clipper or wire snip to cut toy parts free.  Be careful a snipped piece doesn't fly into someone's eye, including your own.

If none of this is possible you have no alternative but to have the item cut free.  I do not recommend that you do this yourself.  In any event use extreme caution with sharp objects.  You may also want to kindly ask the perpetrators not to do this again.