Nahant Beach Reservation
Nahant's "Long Beach" is an easy drive from most spots around Boston. I went today and found ample parking ($3 for whole day) and tons of space on the beach. More importantly, the sand is soft, the water is very shallow for a great distance, and there's a lifegaurd. So it is a terrific hangout for families with young children. My 2-year-old had a blast splashing in the 4" waves. Unlike adjacent beaches, Long Beach has a "comfort station." All the better!

Directions:
MBTA: From Haymarket Station to Central Square, Lynn, take MBTA bus #400, 440, 441, 442, or commuter rail, or take Blue Line to Wonderland, bus #441 or 442 (Marblehead). From Central Square take bus #439 to the rotary near the bathhouse.

By Car:Lynnway (Rt. 1A) to Carroll Parkway to Nahant Rotary, then Nahant Causeway to Long Beach at Nahant Beach Reservation.