We love Maui and go back about every two years so we have been there with our kids when they were six and younger. In trying to get discounted prices, don't fall into the timeshare trap. It isn't worth it to give up 1/2 a day to listen to a high pressure sales pitch.
Our kids would be happy just to hang out on the various beaches. We stay in Kihei so we spend a lot of time on the beaches there. We have been on the beaches when there are very few people there. There are some nice little tide pools to explore too. You can do some snorkeling right there. We also like to go down to Big Beach, but the surf there can be kind of rough. It is nice to take some breaks from the beach sometimes. We have a couple of all day beach days and then some 1/2 days on the beach.
You will be there during whale season. It is definitely worth paying to do a whale watch with Pacific Whale Foundation. We always have seen a lot of whales. The naturalists on board are great and during down times they do some great kids' programs. Sometimes we have even gone on 2-3 tours in a week because they are so fun.
The aquarium is right near Pacific Whale Foundation. It is a nice little aquarium that you can do in 1/2 a day.
We haven't been there yet, but we are planning to spend a day in Iao Valley State Park when we go next year. They have hiking, a nature center with displays for kids. I think you can swim near a waterfall too.
The Road to Hana is beautiful, but probably wouldn't be that exciting for a six year old. We did it on our honeymoon and were gone from sun up to after sun down. It was a really long day spent mostly riding in the car.
The drive up Haleakala is also beautiful, but is kind of a long drive. There are some places to stop on the way up, but is pretty much an all day trip. Biking down the volcano is not something you would want to do with a six year old. We were talking to a local who works in the ER. He said they have a huge number of people come into the ER because of accidents biking down the volcano. He said he would never do it just based on what he has seen come into the ER.
Personally, I would skip the Sugar Cane train.
Our kids loved wandering around the little outdoor market and the farmers market in Kihei. They tried fresh coconut juice and loved the shaved ice. Most of our souvenirs were purchased there.
Our kids also loved the Banyan Tree park in Lahaina. Across the street from there is Dan's Greenhouse where you can see their exotic birds and pot bellied pigs that they have. Lahaina has some pretty fancy art galleries and fancy jewelry stores. There are a few neat little shops, but we didn't really spend much time there with out kids. Too many "look don't touch" stores.
Our kids love the luaus too. We have gone to the Old Lahaina luau a couple of times. It is probably the more authentic luau, but not necessarily the best for kids. The Hyatt has a Drums of the Pacific luau that is a lot of fun. Kids are free. We have also been to the Royal Lahaina luau. They have a kids buffet with standard kids' fare if you have a picky eater.
We haven't been with our kids, but the 'Ulalena show is really well done. It might be a little boring for a six year old because it is in Hawaiian, but the costumes, dance, and drums are amazing.
Get the book Maui Revealed. It is one of the best guidebooks I've seen. Lots of info on restaurants and things off the beaten path. Also a lot about the culture of Maui. Be sure to get the most recent edition. The last time we went our edition was older and lots of the restaurants had closed.
Have a great time!!
