Mine are 6 and 2. 6yo has had about 7 nights of sleepovers with GPs over the years (they live abroad so we see them a couple of times a year). But it was just one night at a time and we saw them again in the daytime (it was just for the fun of a sleepover rather than childcare, since we still had our 2yo with us). And I spent 2 nights in hospital when I had dc2, when DH was with dc1.
I breastfed dc1 at bedtime until she was aged 3.5, and I'm still breastfeeding dc2 and I wouldn't be happy to let someone else do the bedtime routine until I stopped, probably around 3.5 as well. She could cope but it's part of her routine and helps her feel secure.