Before I was 6, I drunk a bottle of Harpic - a mixture of potash and caustic soda, used for cleaning toilets. Also drunk a bottle of Windolene - it was pink so it should have tasted nice. So had my stomach pumped twice. Ate worms from the garden and freshly laid tarmac from the road outside our house.
Looking back, I think I was either malnourished or seriously backward.
Probably, neither, just a brighter than average kid, working out how the world works and the do/don't boundaries with less fear than more cautious kids. My older brother did similar things, alcohol (fortunately not mercury) from a thermometer, black mouth from road being re-tarmacked etc, etc. I was the more sensible one, mostly. But obviously not when we were both playing with matches, setting long dried grass on fire in our back garden and then stamping out the flames, daring each other each time to let the fire get bigger before we stamped it out. As you can guess the inevitable happened with my dad coming home to all of the bottom of the garden burn't to a frazzle, along with a row of trees and much of our neighbours garden and the crops in his vegetable plot, but fortunately not his wooden greenhouse. Needless to say that was a beating we both deserved.
My dad was not impressed with the kids finger pointer and each saying he lit more matches and let it burn more until it got out of control.