I'd be happy to leave DD (15 months) overnight with my mum now (not that that's an option because she's in the UK) but any other family member, NO. Not that I don't trust them but because I would hate DD to feel scared, worried etc. when she woke up in the morning and we weren't there.

I can't imagine going away for a week unless they were at an age where I could tell them what was happening and knew that they understood that it was only temporary. So I guess around 5 or 6ish maybe.