I'm the family cruise editor here and thought that you would like to know that Princess Cruises no longer accepts children two years old in their youth program. They have increased the minimum age to three years old -- and children still have to be potty trained.
If you're looking for youth programs for those under three years, go with Carnival or Norwegian Cruise Line. Disney has a nursery (must pay a fee) for those under three years old.
Luisa Frey Gaynor