The Whydah Pirate Museum displays finds from the wreck of the pirate ship Whydah, sunk off Cape Cod in 1717. The museum claims, not implausibly, to hold the only authenticated pirate treasure in the world: gold and silver coins, jewellery, weapons, and a ship's bell inscribed "Whydah Gally 1716" that conclusively identified the wreck when it was discovered in 1984.
The exhibits are well-presented and aimed at families, but the underlying history is genuinely interesting: the brief golden age of piracy in the early 18th century Atlantic, the social dynamics that drove sailors to join pirate crews (better pay, more democratic ships than naval vessels), and the violent ends that almost all pirates came to. The main attraction for children is a hands-on section where you can handle replica artifacts.