Last year one in every five parents ordered to pay child support did not make a single payment.

Many others made only partial payments. After years, many custodial parents and children simply give up.

But there are surprising ways to recoup back payments - with interest - even after decades.

Family photos bring back happy and sad memories. Sam and Lina Bragg divorced after 17 years of marriage and two children.  He was ordered to pay $200 a month in child support. Lina said she never saw any of that money.

Tax documents show she worked three jobs earning $11,000 a year. Things were tight in their Spring Branch home.

But now she may be getting that money, even though their children are 45 and 42.

“Child support just doesn’t expire,” Guardian Child Support owner Francis Welch said. Guardian is a private child support collection office.

Many wrongly believe child support obligations vanish when a child turns 18.

In fact, finding people and recovering money tends to get easier - as folks age.

“They’ve settled down, they start to leave a paper trial as well as they accumulate assets,” Welch said.

And start new families.

“There is the make-it-go-away factor,” Welch said.

But phone calls, liens and other tactics produced no response from Mr. Bragg. who was a skilled tradesman. Now, Guardian will go after his Social Security.

“That is probably what will happen in the next three to four months, I’m quite confident,” Welch said. She said they’ve done that before.

“Isn’t that nice,” Lina said.

KHOU-TV called Mr. Bragg, who still lives in Houston, to ask about garnishing his Social Security. He said he didn’t believe it and hung up.

Bragg is 72. For now, targeting Social Security checks is uncommon, but as baby boomers age: “in the future that’s definitely going to change, particularly as people take Social Security out a little bit sooner,” Welch said.

Then there is the power of state-required compound interest. The Braggs divorced in 1976. Today, the principal is $17,000. But the interest? Nearly double that for a grand total of $49,000.00 But many, including Ms. Bragg’s children, say leave things alone.  “They just want to forget it,” she said. “No, I’m not. … He owes me the money.”

Private child support agencies charge on contingency basis; typically one-third of what they recover.

The Texas Attorney General’s office said 64 percent of the parents in its current one million child support cases did make all required payments last year.