Michael Snyder, 43, also known as "Mr. Mike," was taken into custody about 7 p.m. as he was picking up his children at the Boys and Girls Club in San Clemente, authorities said.
Snyder's alleged victim went to her mother, who then called authorities Wednesday.
"It was definitely not a one-time occurrence, it had been going on since last year," said Jim Amormino of the Orange County Sheriff's Department.
Authorities did not say how Snyder first met the alleged victim, but said they are concerned that there may be more victims because of his occupation.
Snyder had spent years publishing his poetry and illustrations.
In addition to writing kids' books and performing at schools and libraries, Snyder also runs a company called Independent Living Program.
"He has a business that contracts with a state agency, goes to people's homes, provides services for the mentally disabled," Amormino said.
Authorities spent hours collecting evidence from Snyder's home in San Clemente on Thursday.
Neighbors said he and his wife adopted their teenage son and daughter from China last year.
"Like a regular dad, they take these kids everywhere," said neighbor Elisa Luna. "Every weekend, they spoil these kids. The kids are very happy."
Other neighbors also said they couldn't believe it.
"Furthest thing from my mind," said one neighbor, who identified himself only as Bill. "Fine person, as far as I know."
"I think it's the wrong guy," Luna added. "I don't' believe he could do nothing like that."
Snyder was being held on $100,000 bail on suspicion of child molestation.