We got bunks for DS1 and DS2 at Easter this year - at the time DS1 was 4y1m (top bunk) and DS2 was 2y3m. DS1 has never had any dramas going up/down ladder in light or dark. He's been perfectly fine to sleep in the top bunk. Plus there are two railings 100pc preventing him from rolling/falling out. DS2 worked out a month or so ago that he could climb the ladder up ... but he won't come back down (not sure if it's lack of ability or just scared - the latter, I think).

One thing to note though ... bunk beds are a b*tch to make - especially when one long side is against a wall as ours is. Takes us AGES to undo and remake the bunk bed.