Your boys couldn't squeeze through the balcony rail because it is solid Plexiglas. The Plexiglas however is not crystal clear so I would have concerns about them climbing on a chair or table to "look over" the top of the rail and falling off. Kids have lots of curiosity and not much forethought about the consequences. Keep an eye on them at all times. Yes there's a latch on the balcony door but once again, a chair will give them the needed height to open it easily. The good thing is that your cabin is only one room so unless you're in the bathroom, they will be in your sight at all times.
Renee - The better half of RobRen :-)
Carnival - Spirit: Alaska (August 8, 2007)
Carnival - Miracle: Exotic Western Caribbean (April 9, 2006)
Royal Caribbean - Explorer of the Seas: Eastern Caribbean (January 2005)