Ms. McKean and her son were playing kickball in a shallow cove behind Ms. Townsend’s home, where they have been staying during the coronavirus pandemic, when one of them kicked the ball into the water, said David McKean, Ms. McKean’s husband and the boy’s father.

“The cove is protected, with much calmer wind and water than in the greater Chesapeake,” he wrote in a Facebook post. “They got into a canoe, intending simply to retrieve the ball, and somehow got pushed by wind or tide into the open bay.”

He described Gideon as a compassionate boy who could spend hours reading and loved sports. “I used to marvel at him as a toddler and worry that he was too perfect to exist in this world. It seems to me now that he was,” Mr. McKean wrote. “Maeve turned 40 in November, and she was my everything.”

A concerned citizen who called 911 from the Columbia Beach community pier at 4:30 p.m. reported seeing two people in a canoe “drifting in the bay,” according to the Anne Arundel County Fire Department.

Boats, dive teams and helicopters from multiple law enforcement agencies began searching the bay, the authorities said.

Around 7 p.m. on Thursday, an overturned canoe matching the description of the one Ms. McKean and her son had been using was found, the Natural Resources Police said.

The agency said it had suspended the search for Ms. McKean and her son on Friday night but would resume on Saturday morning.