Waikiki Aquarium

Waikiki Aquarium is in a lovely area of Waikiki. Just outside the aquarium is a large banyan tree where kids can pretend to be tarzan. Inside the aquarium is a grassy lawn where they can play. The Hawaiian monk seal exhibit and tidal touch pools outdoors are nice. Inside is a small aquarium with tanks that have been designed beautifully. All different kinds of ocean environments are explored. The jellyfish exhibits are a favorite with kids, as is the big tank full of sharks and scary-looking fish. Kids like to sit in the circular window to watch the sharks swim by. You can also see an exhibit with sea horses. Some of the tanks have the most gorgeous tropical fish, of colors and patterns you've never seen before. One has a Peppermint Angelfish, a very rare fish that, in all the world, is only on display here. Splurge and buy your child a little stuffed animal of a dolphin or shark at the store at the end of your visit- no, I wasn't paid to say this!- my son loves his stuffed shark!

To the south of the aquarium there is Hau Tree Beach- some call it San Souci Beach- that is lovely for a swim with kids. It's very sheltered and there's a ton of wonderful shade in the morning created by the high rises behind.
Just outside the aquarium, a promenade on a lava-rock wall begins. The views of the Waikiki skyline are lovely from there, and you can walk past Queens Beach (a gay stretch of Waikiki Beach) and all the way to Waikiki Beach near Kapahulu Avenue, a great bodyboarding spot.
Other nice spots in Waikiki from west of here are:  the ocean swimming pool, a safe spot for more timid swimmers, and very romantic at night with the moon shining on the still water; Duke Kahanamoku Statue Beach, in the center of it all; the Sheraton Beach, crowded but with great swimming; and all the way west before you hit the harbor, my favorite spot, the Hilton Hawaiian Village Beach, with tons of fun stuff for kids to do.
Waikiki Aquarium is a good rainy day activity. Another great one is Children's Discovery Museum.
To prepare for your trip, read about animals in Hawaii with your kids. Kids love these little books by Ellie Crowe: Sleepytime Yawns in Hawaii, Seashore Touch-N-See Hawaii, and Go to Sleep, Hide and Seek, about where animals sleep.

Directions

Park along Kalakaua Ave near the aquarium. The parking is metered and costs 25 cents per half hour, and it can fill up on weekends (you will need quarters for the parking meters).
Waikiki Aquarium, call (808) 923-9741. Cost is $12 for adults, $8 for local residents and military, $5 for seniors, $4 for teens, and $5 for kids aged 4-12. Children under 4 are free.
Open daily 9-5.
For beachgoers: There are showers at Hau Tree Beach, and restrooms at the nearby natatorium.

Click on map for interactive view