The trundle beds are small with a thin mattress, however my DD was 12 the last time she slept in the trundle bed and she was fine. I think it was mostly because it was either the trundle bed or sleep with her brother. LOL!!
In all seriousness the trundle beds are not much but they do provide an extra sleeping space at no cost and are all right for a child but don't expect much, they are not anything like the normal trundle beds that roll out from under the bed and pop up and are the size of a twin bed.