Maui has the best beaches in Hawaii, so there will be plenty to do. Look around Paia, Kihei and Lahaina as there is decent "nightlife" (a relative term, the nightlife in Hawaii is non existent outside of Honolulu) and several good beaches around. Avoid Wailea as it's the most expensive area in Maui. I've lived on or visited every island in Hawaii, and Maui is still to me the best island of the lot when taking everything into account (ease of use, good beaches, good restaurants, natural beauty, etc) for visiting... I'd probably rather live in Kona/Big Island.
The drive up to Hana is really cool, and you're never far from sleepy old beach towns. A few tips, Monkeypod by Wailea has the best drinks on the island; Ululanis has very good shaved ice (make sure to order one of the "natural flavors"); Tin Roof & Star Noodle were the two best restaurants I've ever eaten at in Hawaii and they're both on Maui. May is a great time to go as it's not nearly as crowded as it is right now and the waves will be mellow for snorkeling, paddle boarding etc. It's a great trip, and a great island for little kids. I just need 10mm more and I can retire peacefully to Paia, le sigh