One option is to put Solid State Relays in the feeds to your machines. These
take a very low current to activate (3 - 30vdc at several milliamps each) A
small wall wart can run a bunch of them. You can even run these off of CMOS
chips. Then you can selectively turn on machines as your kids get old enough to
use them. My grandfather did that with me (just with verbal warning) and I
still have 10 fingers.