Beaches at Punta Rucia [1] are mostly utilized by Dominican families and have, for the most part, remained a well-kept secret from regular tourism. All along this stretch of the northern coastline, the further you get from Puerto Plata [2], the cheaper and more bountiful the seafood seems to get.
Feast your eyes and your bellies. There are many food stalls lining the beach. Walk around and pick the freshest looking and ask for the best price. They will prepare it for you and direct you to a table on the beach. Options might include fresh king crab, cooked over an open fire (RD$200), and lobster (RD$250).
Playa Ensenada is a one-kilometer-long stretch of nearly white sand surrounded within the embrace of a mountain range. Its waters have gentle waves due to offshore coral reefs keeping breakers out, making it a great spot for kids to play.
Links:
[1] http://www.moon.com/destinations/dominican-republic/the-north-coast/west-puerto-plata/punta-rucia
[2] http://www.moon.com/destinations/dominican-republic/the-north-coast/puerto-plata-and-playa-dorada