Our bunk bed warning label says not for kids under 6 years old. That being said, my DD4 sleeps in the bottom bunk while her sister (who is 8) sleeps in the top. I would not feel comfortable with DD4 being in the top bunk, but that is because she has a habit of getting up in the night to use the bathroom or to come see me if she has a bad dream. She also typically sleeps with her feet hanging off the side of the bed (there are rails on the top bunk, though). She also tends to be restless on vacation, so that would worry me as well. Not to say it wouldn't work for you, but it wouldn't work for us if DD4 had to be in the top bunk. She is allowed to climb up there and play in the daytime, but I don't want her trying to negotiate the ladder in the dark while she is sleepy.