If you are about to head home and haven't had any luck with your snorkeling, set your camera on underwater or "through glass" and head for the Maui Ocean Center at Maalea Harbor. It will cost you about $25 a person, but given the prices for everything in Hawaii, I guess that helps pay for the upkeep of the place. The Reef exhibits have the greatest number of colorful fish with very good explanations of the environment and various species. It was nice to finally see some of the fish I'd hoped to see at Molokini.
While you can pay even more for guided tours with a naturalist, the self-guided tour with occasional presentations at various tanks is certainly adequate, assuming you are willing to read. The audio tour (phone) costs $3 and I stopped using it after the first couple of stops.
The underwater tunnel with huge stingrays, sharks, and other large fish varieties swimming next to you, below you, and over your head is quite impressive. You can literally stand nose to nose with a stingray that has decided to settle against the tank side. The turtle exhibit is a tad pathetic, which was strange since they were apparently running a "turtle month" with added expensive "special" tours. Maybe they'd moved all the turtles somewhere else for the month because there were only a couple of small turtles that spent most of their time hiding.
There's also an outdoor tank with "touchable" starfish and other critters and an interesting tower filled with anemones. Another set of rooms is devoted to the interaction between ancient Hawaiians and the sea, and another to plaster models of whales and sharks--not particularly interesting.
The self-guided "tour" ends at a snack bar, gift shop, and restaurant so if you have any money left at all after your vacation, you can manage to spend it before you leave. If you want to show the kids a lot of colorful and interesting fish and sea critters, this is certainly worth the time and money.