NCL is a family-oriented cruise line, with lots of parent-and-kids activities, a great children's program and even group babysitting until the wee hours. The Kid's Corner, located forward on Deck 7, is a series of three rooms with age-appropriate activities in each. What's really fun about the space is that you have to go down stairs to get to the rooms but there are viewing "portholes" for parents up above.
The Splash Academy groups are broken down by compatible ages: 6 months to 3 years, with parent, 3 to 5, 6 to 8, and 10 to 12. A lot of time is devoted to outdoor activities ("so they can expend energy," the cruise director told me), and there are pizza-making parties for parents and kids and even a child-sized Chocoholic's Buffet arranged in the Pacific Heights restaurant concurrent with the one for adults. The program is free of charge; there is a nominal fee for after-hours group babysitting; plan on about $6 per hour, plus $4 per hour for each additional sibling.
Teens have their group activities, and a disco is set aside specifically for that age group (13 - 17).