21mth child climbing out of bed and sitting on deep windowsil ADVICE PLEASE

[randomama]

Hi our boy 21 month is a real climber. I put him in bed tonight and he snuggled down but then after i left the room i heard a noise and i went in and he was on the windowsill. we live in a house so it's upstairs and a very old house so the windows are not double glazed and the windowsills are deep and 'sit-on-able'. I need him to NOT do this. How do I get th message across so he will STOP?
Any advice will be considered but we don't want to smack him. What I did was pull him off the windowsill and put him firmly in bed and said "no you must go to sleep" but i don't think this is gonna put an end to it.
HELP PLEASE!!!
Thanks

Put him back in a cot until he's older. My dd is 3 in May and I won't be putting her in a proper bed until then at least. There was a lady in Yorkshire who's young dd (about your ds's age) climbed out of her bed and squeezed through the skylight and was seen on the roof by a neighbour! Luckily the fire brigade got her down and it was very lucky she didn't fall.

Unless you have other kids who need the cot, my advice would be to return him to that. I think children under 3 are still very vulnerable and can get up to all sorts while you are sleeping soundly. I'd be worried to death about my dd if she could just wander around.