With so much to do for kids aboard today's jam-packed megaliners, your brood — from toddlers to teens — would have every right to be miffed if they were left behind while you sailed the Seven Seas.

Kids at sea are not an afterthought but, for many lines, an essential part of the cruise picture.

Carnival Cruise Lines, for instance, expects to carry more than 600,000 kids aboard its fleet of 22 ships this year — a six-fold increase from just a bit more than a decade ago.

More than a third of the passengers aboard each Disney Cruise Line sailing are kids under 18. In fact, Disney built its fleet of two 2,700-passenger ships primarily around kids and its family of trademark characters such as Mickey and Minnie Mouse and Goofy. Even lines you might not expect to be especially kid-friendly, such as upscale Celebrity or Crystal Cruises, have initiated special programs and allocated separate spaces for the current generation of millennials.

Among the grandest playpens at sea will be Carnival's two-level 5,500-square-foot kids area aboard its new Carnival Splendor, which debuts in July. This will be the largest play area ever featured aboard a "Fun Ship," according to the line.

As part of a retrofit program, Carnival also is rolling out a new aqua park on select ships featuring a 300-foot-long twister water slide, dual-lane racing slides and water spray apparatus.

Though focused on fun, Carnival has not forgotten that kids don't necessarily care about fine food and, consequently, has created a special menu for its younger passengers, such as jelly chicken nuggets. The line even has a children's turn-down service offering freshly baked chocolate chip cookies at bedtime.

In order for parents to enjoy their cruise vacation and get some private time, Carnival also offers baby-sitting services: $6 per hour for the first child and $4 per hour for each additional child in the same family. (Even on luxury Crystal, baby-sitting fees compare favorably, ranging from $7.50 per hour for one child, to $10 per hour for two children and $12.50 per hour for three children.)

Disney, as you would expect, is no slouch when it comes to entertaining kids (of all ages).

A child-friendly oasis, themed to Capt. Hook's pirate ship, contains a play area with slide and rope bridge, a "captain's closet" filled with costumes, toys and games, and an open seating area for arts, crafts and movie watching. It is designed specifically for kids ages 3 to 7.

Older kids ages 8 to 12 have a science-themed Oceaneer Lab to themselves. Twinkling starlike lights and giant planetary spheres fill the room along with an oversized Buzz Lightyear figure. Even teens get the Disney magic touch. The Stack aboard Disney Magic and the Aloft aboard Disney Wonder are packed with comfy couches, a soda bar serving soft drinks and smoothies, Internet access, plasma-screen TVs, MP3 players loaded with popular music, board games and other chill-out necessities.

The line also has its own take on kid's cuisine. Kids can learn about one of the most famous Mexican desserts, the churro — a sweet, crunchy delicacy — by experimenting with different toppings of their own creation. Kids also can learn about the history of bread, in part, by creating their own loaves of "pan de muerto."

Other lines team up with specialists in children's entertainment or education to set themselves apart. For instance, in 2006, Celebrity Cruises aligned itself with LeapFrog SchoolHouse, widely recognized for interactive electronic education programs for pre-kindergarten through 8th graders, to provide younger passengers with engaging, multisensory learning tools and instruction.

Kids enrolled in Celebrity's "Fun Factory" will be entertained with hands-on activities, games, crafts and other interactive sessions, paired to itinerary and ship. For cruises south of the border, for instance, Celebrity's kids' programming includes learning about sun-dials, making their own pinatas, identifying the Mexican states, creating a scene featuring Pacific Coast sea life and designing their own mosaic frescoes. As for partnerships, Royal Caribbean International teamed with MTV's enormously successful Nickelodeon channel for a first-ever Nickelodeon cruise sailing from Miami Aug. 10 for a Western Caribbean voyage aboard Freedom of the Seas, the world's largest ship, with more than 4,000 passengers.

The kid-friendly cruise will offer Nick-themed activities such as live game shows featuring the trademark Nickelodeon slime, visits with kids' favorite Nick characters such as Dora the Explorer and SpongeBob SquarePants, appearances by the network's live-action stars and more.

For details, contact a travel agent or visit individual cruise line Web sites: carnival.com; celebritycruises.com; crystalcruises.com; disneycruise.com; royalcaribbean.com.