Then your wife is dumb as **** if this she thinks it's your fault. At least it wasn't the head.

Unfortunately children are clever and can figure out how to get into things. While securing potentially dangerous equipment is the first line of protection. He is also old enough to have been taught how to use it under supervision safely. Then unless it was his intention to harm himself, he wouldn’t have hurt himself. Also by teaching him how to use it, it would have taken some of the mystique and lure out of it. Unfortunately for you, your wife feels the need to blame someone and you are the convenient one to blame. It’s easier for her to do that than to blame herself for not watching her son closely enough to have prevented it herself. All I can say is that fortunately your son will recover and your wife will likely recover her senses. Some things you can prevent, some things you cannot. When I was a boy I learned to use my grandfather’s tools - though when I was young I was only allowed to use his hand tools. I used them under his supervision and learned woodworking and carpentry that way. Training and education in how to use things is every bit as important as keeping them secured. This applies to all potentially hazardous things.

Not a locked box? How did your kid get in a locked garage? Not sure your wife is wrong.

and clearly none of that mattered so how exactly did it protect anyone? maybe you should've kept the kid under something called parental supervision

Go put the power tools in a storage locker until he gets older, and settle for normal non-power ones. Kids are tiny ninjas who LOVE to try to play with forbidden 'toys'. Yours is just expert-level ninja powers.