DS was changed very abruptly at about 21 months as I had SPD and couldn't manage the cot, plus wanted him out before DD arrived (due when he was 2) - my mum had come over to help and we all realised we needed to seize the moment! There was no warning, no prep, just one morning he got out of his cot, then by naptime we had a bed in there & the cot was dismantled (no space for both). We were all so prepared for him to struggle but he actually slept better in the bed than he had been sleeping in the cot - he'd been tending to thump & bang in the cot. Seeing him travel around the bed as he sleeps I realise he was actually really cramped in the cot. We've got bed rails on and the bedroom door shut (high door handles) so it still isn't a free-for-all in terms of running around the house. Oh and he LOVES his big boy bed (it's actually a king single, so very big for a toddler boy!!).