LONGHUI COUNTY, China — Many parents and grandparents in this mountainous region of terraced rice and sweet potato fields have long known to grab their babies and find the nearest hiding place whenever family planning officials show up. Too many infants, they say, have been snatched by officials, never to be seen again.

But Yuan Xinquan was caught by surprise one December morning in 2005. Then a new father at the age of 19, Mr. Yuan was holding his 52-day-old daughter at a bus stop when a half-dozen men sprang from a white government van and demanded his marriage certificate.

He did not have one. Both he and his daughter’s mother were below the legal age for marriage.

Nor did he have 6,000 renminbi, then about $745, to pay the fine he said they demanded if he wanted to keep his child. He was left with a plastic bag holding her baby clothes and some powdered formula.

“They are pirates,” he said last month in an interview at his home, a half-hour trek up a narrow mountain path between terraced rice paddies.