"What's this?" my 5-year-old asked, picking up a square, black object she had found washed ashore on the beach.
"I don't know," I responded immediately (and automatically, as parents sometimes do).
She shook the plastic-like object, which had a thin strand of thread sticking out from each corner, and heard something rattle inside.
"Maybe it's still alive," she said, hopeful but puzzled.
"I don't know," I said again.
It didn't take long for me to realize I had come to the beach ill-prepared to handle a barrage of questions from my children, who were curious about shells on the shore, birds in the air and dolphins in the surf.
Only later, during an afternoon trip to the Visitor's Center at Assateague Island National Seashore, did we solve the mystery of the black object. It was, we learned from naturalist Rachelle Daigneault, a skate egg case.
"They're called a mermaid's or a sailor's purse," Ms. Daigneault said.
The skate, we were also told, is a fish of the ray family, but is not harmful.
The rattling noise my daughter heard was probably sand or tiny shell particles caught inside, Ms. Daigneault said. The thin lines are used to hang onto seaweed on the ocean floor.
"It's doubtful an embryo was inside," Ms. Daigneault said. "I've found lots of them over the years, and only once have I ever found an embryo."
While the miles of shoreline along Ocean City afford great opportunities to find shells, horseshoe crab shells, egg casings, starfish and other examples of marine life, beachgoers may find it difficult to identify these beach offerings.
But there are several avenues available to help parent and child learn more about the beach and marine life.
First choice is Assateague Island National Seashore, a natural classroom where young and old can learn about wild ponies, birds, shell and surf fishing and the beach environment.
The Visitor's Center, off state Route 611 just before the bridge to the island, is a good place to start.
Inside is a hands-on open tank containing horseshoe crabs, spider crabs, large snails with pear-shaped shells like the channeled whelk, and tube worms. Yes, children can handle them all.
There's also an aquarium featuring sea urchins, summer flounder, spider crabs and other marine life. No, children can't touch here.
Besides the aquarium, the center features another hands-on exhibit -- a reconstructed beach filled with marine debris, including a skate egg case, shells of mussels and clams, and skulls of dolphins, wild ponies and deer.
"You see fewer kinds of shells here but more of them," Ms. Daigneault said. "In the South, you see more kinds of shells but fewer of them.
"[Shells] are not as colorful here, either," she added. "That's because things live inside and must camouflage themselves with this environment."
Some of the more common shells beachcombers will find along the Ocean City shoreline include the surf clam, a large, sturdy shell with fine concentric lines, and the common blue mussel, a thin shell shaped like a rounded triangle, colored black-blue outside and white inside.
Most shells, we learned, are washed ashore during winter tides.
Perhaps the best way for your children to learn more about the beach is without you. Let them explore Assateague's beach with naturalists through the "Kid's Beach Discovery."
The 90-minute program takes children, ages 6 to 11, on a guided tour of the beach, where naturalists point out seashells and marine debris, sift through the sand to point out various particles and play beach-related games.
"Most kids get something out of it," says Jeanine Ferrence, a park volunteer. "Most kids find it interesting."
The program begins at 2:30 p.m. Tuesdays, Thursdays, Saturdays and Sundays on the beach of the northernmost boardwalk leading from the North Ocean Beach parking lot.
There's also a "Seashore Ranger Program" for children ages 6 to 11, which allows them to explore the island on their own (with parental guidance, of course). Activity sheets can be picked up at the Visitor's Center, and participants must attend at least two scheduled programs, which range from surf fishing demonstrations to aquarium feedings, to complete the sheets and earn a certificate and pin.
Naturalists, too, can answer questions about island mammals and other marine life, such as bottlenose dolphins (frequently seen swimming in schools not too far offshore) and brown pelicans, birds believed not to be native to this area but who have been nesting at Assateague for several years.
The park also features other programs, including strolls through the forest and marsh to spot birds of Assateague and wading in the bay to take a close look at marine organisms.
Other opportunities to see marine life in the area include the boat O.C. Princess, which features nature cruises to see dolphins, whales and birds. And the Fisherman's Wharf Marine Center in nearby Lewes, Del., offers morning and mid-day dolphin watching and an afternoon whale watch.
Assateague, cruise information
For more information on Assateague Island National Seashore and its programs, call the Visitor's Center at (410) 641-1441.
For more information on the O.C. Princess cruises, call (410) 213-0926. Cruises are from 4 p.m. to 7 p.m. Tuesdays to Saturdays.
For more information on the cruises offered by the Fisherman's Wharf Marine Center, call (302) 645-TUNA. Cruises depart at 9 a.m., 11:30 a.m. and 2:30 p.m.