The charity had helped 2,128 children by the end of June, about 80 percent of them living in Fujian, and the number of its volunteers had grown from 30 at the end of 2014 to 800.

But Lin said he still encounters difficulties when trying to help inmates' families. "One challenge is to persuade inmates and their family members to give more information about their children, while another is raising money to operate the organization," he said.

To illustrate the first challenge, Lin shared the case of a man sentenced to life in prison for intentional injury in 2014. The man applied for aid from Red Apple.

"We didn't effectively help his three children as he couldn't give sufficient information about the kids, and his wife, a waitress in a restaurant, didn't cooperate with us," Lin said.

When he met the wife at the address provided by the inmate, he found the three children did not live with her. "The family qualified for aid, but the woman was reluctant to talk about the children, just telling me that the oldest one－a daughter, then age 17－lived in a school dormitory," Lin said.

When he reached the girl, she had not been in school for several days because she was worried her classmates knew her father was a criminal. She returned to school after being given psychological and financial aid by Lin, but her two brothers were less fortunate.

"We got little information about the boys, as the mother refused to answer," he said. "Later, we were told by the family's neighbors that the older one had been jailed for stealing motorcycles, and the younger one had dropped out of school."

When Lin tried to get more information from the mother to follow up and help the boys, her phone had been disconnected.

"Some criminals' family members feel ashamed to be related to inmates and don't want to work with us," Lin said. "Meanwhile, some other people often label the inmates, believing they and their children are bad people."

Lin designed a four-day camp to bring inmates, their children and other family members closer, hoping the adults and children would learn to understand each other better by painting and playing games together.

But the program was only held three times last year and once this year because some inmates' families cannot afford to travel and Red Apple lacks the funding to help them.

To boost its finances, Lin has been urging the public to donate online, highlighting the significance of the aid it provides.

He said children's smiling faces motivate him to keep the organization going, adding that the support of his own family is a constant source of encouragement. Last year, he got a birthday card from his 16-year-old daughter that read, "Daddy's job is valuable, and I'm proud of you."