Aloha: I am a Native Hawaiian, born and raised on Maui and just last year, my family and I went on the Molokini tour and loved it. I get sea sick too but it never happened that day. The people on the tour were pleasant and very helpful. Swimming among the fish, turtles, was the hight light of our trip, including for my husband who is a fisherman in his own right. Take water proof cameras ( may be able to buy in bulk at Costco, which is right on the road that leads out from the airport) and enjoy yourselves - you won't regret it.
I live in Hana so I don't know where you and your family will be staying while on Maui, but if you drive to Hana, start really early with a packed lunch or decide to eat here in town if you want to. While driving on the road, it is expected (not everybody does this) for you to pull over when a car comes up behind you (courtesy). For our local people, we travel that road for emergencies, shopping for the day, business appointments, etc. and we usually need to get over and back home in the same day, so it is greatly appreciated when cars in the front of us pull over so that we can pass.
As for things to do with your family, the events are endless. Again, I don't know where you are staying, but all the hotels have something to do for all families and there are lots to do in different areas of Maui, depending on whether you are outdoors people are not. So, welcome to Maui, and have a blessed and pleasant time while you are here. Psalm 91 over you and your family with God's promise of long life and protection. Aloha and Mahalo, Frances M. Kalaola, Hana, Maui