DD now 4 was 3.8 when she was moved out of her cot (well it was a cot bed but with the sides still up).
I had tried 6mths before and after 10 very sleepless nights with her making a dash for freedom and every opportunity I caved in and the sides went back up.
I told her when she was a big girl and would not run round the house in the night when everyone else was sleeping I would take them down again.
She has had the sides off for about 4mths now.
(She was not dry at night when sides were up so did not need to get to loo etc).