Pierce County Sheriff's Office spokesman Ed Troyer said the clothing on the body matches that of 8-year-old Azriel Carver, who disappeared along with his mother, Shantina Smiley of Silverdale.
Troyer said the Pierce County Medical Examiner will need to determine the cause of death.
The body was found Thursday afternoon on the south end of Fox Island, near Paiute Road, by a woman who was out walking her dog on the beach, Troyer said.
The Fox Island beach near where the child's body was found is seen in this photo.
"Yes, absolutely," he said, when asked about the possibility. "The Dana Passage goes right up that way," Mealy added, referring to a tidal system between Olympia and Tacoma.
Troyer said deputies are now out searching the beach in both directions for any sign of Carver's missing mother, Shantina "Kat" Smiley, 29.
In addition, a Coast Guard craft and Pierce County sheriff's boats are out searching the waters around the island.
Carver vanished Saturday night, along with his mother, Shantina "Kat" Smiley, 29, while on their way to Castle Rock from Silverdale.
Deputies have been searching for the missing pair ever since their minivan was found submerged in a small cove off Budd Inlet near North Olympia, with the doors open.
Bloodhounds also have searched the roads and the area surrounding the beach, but were unable to pick up a scent.
Deputies did recover several items that washed up on the beach in Budd Inlet on Tuesday night that belonged to Smiley, including leather shoes, an inhaler and an orange ball. A half-full and corked wine bottle also was found.
The missing boy's father, Jay Carver, was on the scene of the search Thursday near Olympia, hoping for any signs of his son. Carver flew in from Buffalo, N.Y., late Tuesday night in hopes of aiding searchers.
He said his heart sank when he heard the news that the boy's body had been tentatively identified.
"I was just hoping to find them safe somewhere to where I can come through and have them, and find them alive ... didn't play out that way," he said. "He could've offered a lot to this world. It's just a shame that he's not here." Smiley and her son were headed to her stepfather's home when they disappeared over the weekend.
"It's almost like she vanished out of thin air," said stepsister Chelsie Woodard, 32, of Castle Rock, whose father used to be married to Smiley's mother.
Detectives have determined that Smiley turned off Interstate 5 in the Olympia area while enroute to Castle Rock, and was seen by several people who described her as appearing to be confused and lost.
A wallet containing Smiley driver's license, some cash and credit cards were found in the minivan, but neither Smiley nor her son was anywhere in sight.
"Apparently she got stuck and abandoned the car," Mealy said. There was no indication that a crime took place inside the 2005 Dodge Caravan, he added.
An employee at an east Olympia diner where she bought a corn dog told investigators that Shantina left without her purchase and then tripped and fell walking back to her van, but Mealy said the fall was not serious.
The elderly couple who lived nearby said they let Smiley use their phone to call her grandfather, gave her son a piece of pizza, and then directed her back to the freeway. She wasn't heard from again.
Mealy said that as she left the home, Smiley made another series of driving errors that eventually led her to a hard-to-find dirt path and driving onto the beach.
Friends and family described Smiley as a responsible, mature, rational woman.
Smiley's fiance, Robb Simmons, and Smiley's stepfather began searching for Smiley and her son after she didn't arrive at their planned meeting spot Saturday. Azriel was a second-grader at Vinland Elementary in the North Kitsap School District, according to school principal Charley McCabe.
Earlier this week, Smiley's fiance said the woman had a drinking problem and relapsed last week. However, Robb Simmons doesn't believe Kat would do anything to endanger her son.
"To think that she would be drinking on the road with her son, that's an insane idea. I don't believe that would happen," he said.