Every school day after three in the afternoon - so, half an hour ago (it being 3:30 pm here in Australia GMT+8).
I can't speak to your 11 year old, but I'm happy leaving my grandkids with money .. typically I've let them (and my kids when younger, nieces, nephews, et al) pull molten glass from a furnace from 5 onwards (with half an eye watching from not too far away), relatively unsupervised after they've left primary school.
First year high school is typically 12 or so (IIRC).
Chainsaws, angle grinders, etc. are definitely a high school thing, as is riding bikes to the beach and free diving with a gidgee .. as long as they bring back fish.
Maybe you might want to unseat yourself and attend to your problems before telling others what to do. Cheers.