6 Best Beaches for Kids in the U.S. and Mexico

A family beach vacation is an American classic. But depending on their children’s ages and inclinations, some families may be drawn to different kinds of shorelines: those featuring clear, calm water for snorkeling and learning to swim; or, for shell collectors and young naturalists, sandy stretches carpeted with seashells or bordered by tide pools. For castle builders, fine sand is a must, while would-be surfers need tidy waves, ready to ride. Here are six great beaches in the United States and Baja California for family-favorite summer activities.

For castle builders: Mission Beach, San Diego

San Diego’s temperate climate allows for barefoot beach days year-round. For those who’d rather build with sand than lie in it, Mission Beach has another advantage: San Diego Sand Castles and the sand sculptor JT Estrela. Mr. Estrela, a former math teacher, offers lessons in the art of sand castle construction on this family-friendly Southern California beach, where the sand is perfect for castle building: The grains are fine but not too silty, clean below the tide line, free of shells and rocks, and pack hard.

In his two-to-three-hour sessions (starting at $160 for two people, $20 for each additional person), Mr. Estrela works with families to build elaborate five-foot-tall castles. The goal is for participants to “feel like this insider of arcane knowledge,” he said.

While the best sand in the San Diego area is at the offshore city of Coronado in San Diego Bay, Mr. Estrela prefers working with families at Mission Beach. Known for its boardwalk amusement park, Belmont Park; historic beachfront swimming pool, the Plunge; and excellent playgrounds, it’s particularly fun for kids. The smell of cotton candy and hot dogs hangs in the air, mingling with shrieks from the Giant Dipper, Belmont’s 1925 wooden roller coaster, squawking sea gulls and salt spray. Its biggest downside is its popularity, which means parking can be a challenge.

In an archipelago known for spectacular beaches, Onekahakaha Beach Park, on the rugged, volcanic coast of the Big Island, may seem a counterintuitive choice. At Onekahakaha, with its two large, sandy-bottomed ocean pools enclosed by lava rock walls and backed by palm trees and an expansive grassy lawn, the sand is mostly below the surface.

Separated from the Pacific Ocean’s notoriously powerful waves and rip currents, the seawater within the pools is warm and placid, protected and shallow, which makes it excellent for little…