Dear Daughter Mary,
This is a great idea, and of course you can make a charm for you and your family members incorporating rocks you found at the beach. One of the easiest things to make would be a mojo bag.
Buy small bags in the favorite color of each person you're making them for. Add the stones from the beach. You can also add black tourmaline, which will create a protective barrier around them, and bloodstone, which would absorb any negative energy. Finally, add a piece of rose quartz, which represents your love of them. When you have all the mojo bags put together, hold them in the palms of your hands, visualize a protective barrier around them, and pour as much love as you can into these bags. Once you feel the energy stop moving, the bags have been charged and are ready to give out as gifts.
Any moon phase is appropriate for this, however, we have a full moon coming up on November 25, which would be a great time to add a little something extra to your spell.