It sounds like a bit of a silly question but the reason why I ask is because we want to change his cotbed mattress (which he has had since he was born) as it has started to dip in the middle but I am wondering if cotbed mattresses are still adequate for 4 year olds (he weighs about 18 kilos).
I don't want to change the bed as it is a good one from John Lewis and it fits DS' small bedroom.