P.M.
My 5 year old is the same. My daughter has the same childhood problem I had - which was being in so deep a sleep, nothing would wake me/her. I took medicine which was meant for short term, but took long term on Dr.'s orders and now I cannot STAY asleep, have horrible sleeplessness even when I do sleep because now EVERYTHING wakes me up.
My pediatrician said they do not begin to worry until 8 years old, and to just use pull ups, diapers or a waterproof mat until she is able to adjust her body.