The discovery prompted lifeguards to post signs warning beachgoers of the potential hazard. In the morning, lifeguards searched the waters and found the young five- to six-foot sharks.
Marine Safety Department officials said the juveniles were not acting aggressively and that is why the beach remained open.
Shark experts said it is common to see predators along the coast of Southern California, but it is rare for Seal Beach.
"This is the first time in the last 25 years that we've had a confirmed sighting of a white shark. We've had reports of sharks," said Chief Joe Bailey with the safety department.
PHOTOS: Sharks, whales spotted off Seal Beach coast
When the animals are spotted, it is usually because the sharks are just passing through the waters and are headed for another destination.
But some residents are concerned.
"It's always something we think about, but to hear it and actually see a sign up it wakes you up a little bit," resident Ryan Riske said.
Other residents said the sightings are just a part of enjoying the ocean.
The department will continue to monitor neighboring beaches for any shark activity.
Anyone who spots a shark is asked to contact the department at (562) 430-2613.