Hi I just did this with dd after xmas. She was starting to lift her knee over the top but never actually got out she was 2.8 and we probs could have left it a bit longer. We were talking about having another baby so decided to get dd a single bed and keep the cotbed and just get a new mattress for that for a new baby.
In actual fact its been great even tho a totally new bed thats slightly higher than her cotbed and of course much longer and wider. She settled straight in the first night but heres the catch...
I know supernanny always says to let them settle themselves down but our routine is that i read her a story and lie on the bed with her till she falls asleep which takes about 10-20 minutes and is usually 9/10 fuss free and straight forward and no stress. I would rather spend 10-20 minutes a night lying on the bed having a cuddle in utter peace than have her keep getting out of bed which I think would be quite stressful and noisy and quite awful. I will at some point change this so she settles herself, when shes a bit older. I know a lot of people would disagree with this method but its easy, no stress and works for us, bedtime is peaceful.
We went with the idea of leaving it as long as possible, thinking she would keep getting out of bed so put that off for as long as we could, however from the first night she slept all night! There are benefits to her being able to get out of bed herself on a morning as she can play and entertain herself until i shake off my sleepy head, tho on this basis i suggest hiding all noisy toys! Also the one thing that would have her shouting for me first thing on a morning is a wet nappy, now she just gets out of bed takes it off and gets on the potty if she needs to. If its really early and shes still tired she just climbs into our bed.
Its all been quite easy and I think the excitement of a new quilt cover makes it all more interesting too! So I dont think leaving it a bit longer will cause any harm but I guess it depends on how well they sleep to begin with, dd slept all night in the cot waking only if the quilt had been kicked off and thats the same for her now unless shes unwell and being a bit older I guess she understands a bit more but im sure people have taken the cot sides off sooner and its been fine, i am interested to hear of other peoples experiences...