I have done about 80 charters in my life in all kinds of configurations, kids, including my son, from age of 3 to 20, etc... I am also a certified captain. I can say with certainty that I would NEVER let a kid sleep in the forepeak, IF the access is from the deck only.
Depends on his/her age of course, but consider this scenario: It's 2 AM, the kid wakes up, wants to go to the bathroom, climbs the ladder to the deck, is half asleep, stumbles and falls in the water while everyone else is asleep? Then what?

You all may say that I am extremely pessimistic, but I am a complete safety freak, especially when it comes to kids. Besides, i have seen too many freak accidents. But that's just me...