It was a ton of fun in the sun Saturday afternoon when dozens of kids let out their inner architect on the sands of Onset Beach for the Onset Bay Association's inaugural Sandcastle Day.

What's more, the kids got some words of wisdom and a demonstration from a master sand sculptor.

"I just want everybody to enjoy their time at the beach," said Rodney Johnson, better known around Onset as "Mr. Sandman."

Johnson was the master of ceremonies of sorts for the sandcastle event. While kids and parents constructed their own sandcastles on the shoreline, Johnson was sculpting a shark out of the sand, complete with colors and prop body parts.

Residing in Brockton, Johnson has been doing sand sculptures at beaches all over the state for the last 10 years, but he said Onset is his favorite.

"This has been like a home base for me," he said. "I like the people here."

The kids who participated in the event all got leis from the OBA and chose a variety of different sandy structures to make. One group followed Johnson's lead and made a sea turtle, while others followed the more traditional route of tiered castles and towers.

One group of kids, who dubbed themselves the "Supercakes," made a birthday cake out of sand, elaborately decorated with starfish, seashells, jewels, and, of course, birthday candles.

"It actually got the kids to work together," remarked one of the parents.

The Sandman had some help making his shark, too. His grandson, Shane, lent a helping hand and sprayed down the shark with water to keep it from falling apart in the afternoon sun.

"I think I'm going to become the Sandman, too," Shane said.

Even though castles made of sand fall in the sea, eventually, Johnson had many admirers and curious onlookers throughout his sculpting process.

"It's pretty incredible," said one passerby.

"It's just different is all," Johnson replied.