They had only been there for about two hours, but already they had built domes, seashell walls, bridges and a double moat.
While her cousins reinforced the structure with more sand, 8-year-old Jadelynn Hintz became a one-girl bucket brigade.
"Get out of her way!" one of the adults shouted.
Ten trips later, the moat sprang to life and water flowed back to the creek.
Before Crescent City got carried away with Independence Day, First 5 Del Norte and the Del Norte Child Care Council invited parents and kids to the east end of Howe Drive for some non-competitive fun in the sun on Thursday.
Armed with plastic buckets, shovels and trowels the kids and their parents spent a sunny and warm afternoon building sand castles on the shores of the Elk Creek estuary.
"We've had a very good turnout," said Valerie Machado, an accountant clerk with the Child Care Council. "I think we have more sand castle building this year."
The Child Care Council has held the event, Sand Castles by the Sea, for more than 10 years, aiming to schedule it on the eve of the Fourth as long as it is a weekday, Machado said.
The event provides a laid-back start to the holiday for local families, out-of-towners and parents returning to their childhood home. Machado said she had at least two people who told her they had come home for the Fourth.
This was the case for Shandra Leis, who brought her husband Robin and her sons, 5-year-old Christopher and 10-year-old John-Patrick, to the coast from Phoenix. Leis grew up in Crescent City and after spending three years away from the area brought her family for a two-week visit.
"My mom is in her 70s," she said. "I haven't seen her for three years."
Leis said she's taken her boys to the beach and to the river, and she planned to go to the Deck Party and do "every Fourth of July thing" on Friday.
To prepare for Sand Castles by the Sea, the Leis family turned to YouTube for tips on how to build a good sand castle. They made a slurry out of sand and water and built up cliffs and walls. When they heard about Jadelynn Hintz and her double moat, the boys ran off to see it.
"I always love the Fourth in Del Norte County," Shandra Leis said. "What a nice thing for the community to do for its kids."
With her sister, nieces and nephews in town from New York, Jacy Hall said the 10 kids building their castle ranged in age from 1 to 15.
"They're from Central New York, where there's no sand or beaches," Hall said, referring to her sister. "I thought this would be a fun thing to do with the children."
Reach Jessica Cejnar at email@example.com.