I go by the strength of the spring - I can't remember how heavy it can go to.

DD used it until she was nearly two, she'd just call out when she woke up. DS rolls over in it when he wakes up, because the tv is behind it and he just rolls over and watches the cheeky bugger lol. I'm not worried about him being able to climb out, by the time he can get to a sitting position on his own and possibly climb out he'll be big enough to reach the ground if he does get out. It wouldn't be easy though, I think I'd see him well before he got out, or if I wasn't in the room I'd hear.