I know Falmouth, Dennis and Chatham have them. More towns than that, check at the town hall. These are the really big ones with ramps, horizontal ladders, tunnels, swings, slides and all kinds of neat stuff . If you are here for July 4, many towns have there own fireworks . One of the neatest ways of watching is to find a central location and watch different towns' fireworks all at once.
Towns also have local festivals where they shoot off fireworks at other times of the summer.
Some of the best places are the big river systems and the salt marshes they come from. Places like Scorton Creek in Sandwich, Chase Garden Creek in Yarmouth, Swan Pond River in Dennisport, Herring River in Harwich, the upper end of Little Pleasant Bay in Orleans, Nauset Bay out from Salt Pond in Eastham, Pamet River in Truro. IF you paddle an estuary at high tide you'll see more country due to your height, at low tide you'll surprise more wildlife around corners. Only a few beaches have lifeguards either fresh or salt. Be cautious and bring an adult.