I've noticed that some children seem to lose every bit of common sense they had when small as soon as hormones start to appear. Sibling fights, flailing hands & tears, stomping feet & cuss words. That behavior was what kept my rotary cutter in my hands.
DGDs had great presence of mind when home alone with dog who had seizures. I still wouldn't take the chance of one of them having a hissyfit with a rotary cutter in her hand. It simply wasn't worth. Now they are both old enough to have jobs and can buy their own.