I agree that a 4 day cruise is just too short. If at all possible, do the 5 day, and get the balcony.
With my kids, at bedtime, my hubby and I would put the kids down, and then the two of us would retire to the balcony. This allowed us some privacy, but kept us close by if we were needed.
RCI Radiance of the Seas Sep 2009
NCL Sun March 2008
Carnival Destiny June 2006
Carnival Ecstasy June 2002
Carnival Elation August 2000
Celebrity Century June 1998
Carnival Carnivale August 1993