My oldest had his first sleep over with my mum when he was about 4 months old, I was suffering from pretty severe PND so it was all about helping me out but I trust my mum completely.
I have one friend who I would trust to have my kids overnight, but no one else just yet. They are 4.5 and 2.5 and they go to my mum and step dads house at least once a month normally.
As for friends houses when they are older... I'm not sure. I guess I won't know how I feel about it until the situation arises.
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