The 4 day trolley pass is the best bang for your buck. Check website for more details.
The Trolley is a great way to get around Waikiki without the stress of driving yourself. Kids under 3 are free to ride. The cost is $2 a person each ride. Kids love the excitement of riding with the openness of the sides. And parents love it cause its stress free. This is definitely the best way to travel down to Waikiki.
The Waikele Trolley is a free trolley that runs between the Waikele Shopping Center and the outlet mall. The trolley makes a big loop through several strewn out parking lots. While the intent is to move shoppers between the stores and restaurants, you will notice many riders with kids not getting off at any stop - they are there to ride the trolley. The trolley is just a fun thing to do when the kids need a wind down activity. Along the way is a Borders (decent kids book section) and a Starbucks (kids chocolate milks are $1.15), and take a bag of quarters because spread throughout the Outlet mall you will find rides (50 cents each of course, but many hold two kids). The Trolley becomes a little crowded on weekends and during heavy Christmas shopping and runs between 10am and 7pm daily.
The open-air Waikiki Trolley is a great way to get a complete overview of the town. The trolley travels to many nooks and crannies of the city, including many of its historic sites. Passengers can get on and off an unlimited number of times. You can make a day of it, exploring, stopping for lunch, and hitting the road again. Tickets are available online, at the DFS Galleria Waikiki, Ala Moana Center (ocean side), and the Hilton Hawaiian Village. Or you can simply board at any one of the stops, and the conductor will sell you a ticket.
My 2 year old son LOVES trains. So, trolleys are high on his list too. For $2, you can ride the trolley from Ala Moana Shopping Center to Waikiki, or vice versa. It's a great way to enjoy some fresh air, see Waikiki and have something for your kids to talk about for days (at least that's what happened for us). The best places to board are Ala Moana Shopping Center or the Duty Free Shops on Waikiki. If you try to get on at other stops, you'll have to hope that someone else is getting off to make room for you.
Also, beware that if you get a coupon for a free bottle of water on the 3rd floor of the Duty Free Shops, you should consider passing it up. Because we were cheap, we went for it, but once you get up to the 3rd floor, it's impossible to get out of the building -- they make you walk through the maze of shops to exit. It probably took us 30 minutes to find our way out. Not worth it for a small bottle of water.