BANGKOK — An 11-year-old bride to a Malaysian man 30 years her senior has returned to her native Thailand, where she is under the care of the local social welfare department.

Ayu, who is being identified only by her nickname for her protection, was married in June as the third wife of Che Abdul Karim Che Abdul Hamid, a Muslim rubber trader from the northern Malaysian state of Kelantan. The case has provoked soul-searching in Malaysia, where the prevalence of child marriage belies the Southeast Asian nation’s modern outlook.

Earlier this month, Thai officials picked up Ayu and her parents in a Thai town on the border with Malaysia, said Surapol Prommool, the governor of Narathiwat Province in southern Thailand. She is now being cared for in a Thai government institution by an all-female staff of social workers, psychologists and doctors.

Mr. Che Abdul Karim has not been allowed to visit her there, Mr. Surapol said.

“For us, the most important thing now is to treat her mental condition,” he said. “We are working to make her calm and feel better.”