The Carnival Liberty cruise ship does have a kids wading pool outside of the children and family center called Camp Carnival. Children are divided up into different age groups and tended to by individual Carnival cruise line staff. The Camp Carnival facility also offers kids the opportunity to play video games, do arts and crafts, read in the library, watch movies or television via the video wall, use the computer lab, or play in the soft-play area. The Camp Carnival facility is approximately 4,200 square feet in all, so it's an enormous play area for children.
For more info, see Carnival Liberty Cruise Ship