errrm I would say no but then I am very anxious about safety and such.
I agree with whensmydayoff on this one. 2 year olds (or at least my 2 year old!) are such babies in many ways, do strangest of things and a 6 year old should not be responsible for them. They open drawers and could trap fingers, could pull cupboards, boxes etc on to themselves, they delve around in the toilet and throw loo rolls down there! uuurrrgh!
I am usually in the same room as my ds and if I go to the toilet he usually comes with me. Would never leave him upstairs without me unless in his cot. Maybe I am overprotective though!