Before You Go
Check on restrictions on collecting. A lot of coastline is not open to the public. You should either be on public beaches or have permission to be on private beaches. Be sure that the state, park, or beach does not prohibit seashelling. Some areas prohibit the collection of certain species or limit the places or time of year you can collect. Check with local officials to see if there are restrictions on shell collecting in the area you're planning to go at the time of year you'll be there. Find out if you need a permit.
Invest in a good field guide. You might even want to choose one that's appropriate for the kids and a separate one for grownups. Reading your field guide with the kids before you go will pique your kids' interest and enhance the excitement of the trip. Once you're at the beach, knowing what kind of shell you've discovered and learning about the animal that lived inside it make seashelling even more enjoyable.
A good guide for kids is Seashells, Crabs and Sea Stars, from the Young Naturalist Field Guides series (Gareth Stevens Publishing, Milwaukee, 1998). It's chock-full of information about many species of sea animals that inhabit shells as well as seashell-related activities and tips.
For guides for grownups, search your favorite online bookseller or bookstores for seashelling books or seashell field guides -- there are good ones that cover the entire country or specific regions or states. And Read EHow.com's article "eHow to Choose a Field Guide for Seashells" for lots of helpful suggestions about looking for guides that are user-friendly, proportioned practically, well-illustrated or clearly photographed. The article also lists several guides that fit the bill.