Nahant Beach State Reservation in Nahant, Massachusetts is a nice swimming beach in the summer.
There are more than a dozen access points to the beach and ample parking along the whole stretch of beach.
The sand is soft and the water is quite shallow a long way out perfect for the little ones. There is a long bike / walking path between the parking area and the beach that is great for people watching in the summer and jogging or dog walking in the off season.
The beach has a lifeguard during the summer season and portapottys at several locations. At the Nahant side of the beach is a nice seafood restaurant The Tides.