An 18-month investigation has discovered an underground network of adoptive parents who are trading or selling children adopted from abroad to complete strangers and, according to one U.S. adoption expert, ending the practice will not be easy.

The Reuters news agency investigation found virtual communities in Yahoo Groups, Facebook, and elsewhere online that were being used by families who are either dissatisfied with their adopted children or unable to cope with them. The parents posted online ads offering their adopted child and then handing them over to strangers, usually with no background check, and without the input of child welfare workers.

The practice is being dubbed "re-homing," a term typically used by pet owners looking for new homes for their animals.

Reuters found one now-disbanded message board on Yahoo Groups in which an average of at least one child a week was being advertised for "re-homing." Most of the children ranged in age from 6 to 14 and around 70 per cent had been adopted from abroad.

The consequences of these unvetted "re-homings" can be devastating. Reuters learned of one girl adopted from China and later sent to a second home who was made to dig her own grave by her abusive guardians. Another girl said, when she was 13, she was re-homed three times in six months.

Chuck Johnson, the CEO of the National Council on Adoption, says the practice of "re-homing" is not new, but has been occurring largely undetected for years.

"We've been aware of this for some time, but in the U.S., the laws dealing with this are quite vague," Johnson told CTV's Canada AM from Washington on Thursday.

Johnson explained that it's not illegal for a parent to transfer custody of their child to another family; in fact, it happens all the time.

As the Reuters report explained, children can be sent to new families quickly through a power of attorney document, which declares the child to be in the care of another adult. Such documents are meant to be used in cases in which parents might be experiencing hard times and need to send their kids to temporarily stay with a trusted relative or other guardian, for instance.

But the investigation uncovered abuses, including parents who are turning to Internet chat groups to recruit strangers willing to take in their unwanted adopted children.

The power of attorney documents allow the new guardians to work around the formal adoption process, which must be handled through the courts, and requires the vetting of prospective parents.

With the power of attorney workaround, guardians can even secure government child benefits or enroll the child in school, with no one aware of illegal change of custody that has taken place.

Johnson said in many cases, the exchanges are done with the best of intentions, by parents who adopted children whose needs exceeded their ability to care for them.

"I would think the majority of the people who are interested in helping these families are good people," he said. But he added: "We're hearing these sites also become a magnet for people who were pedophiles and those who did not have the best of motives."

Johnson says in many cases, the original adoptions took place 10 or 15 years ago, before the U.S brought in better systems of checks and balances into the foreign adoption system. He says these days, prospective adoptive families are better educated and prepared for the challenges of adoption, and are also offered enhanced post-adoption support services. But, he says, sometimes mistakes are made.

"Some families from years ago -- and even families from today -- feel they have nowhere else to go so they have sought out these internet chat groups," Johnson said.

Johnson said he believes that the system of adoption in the U.S. overall is working "very well," noting that more than 2 million children in the U.S. have benefitted from adoption, and are in safe and loving families. But he says more needs to be done.

"These are tragic exceptions and we need to plug this hole," he said

Johnson notes that just last year, the U.S. enacted the Universal Accreditation Act, to ensure that every adoption agency dealing in inter-country adoption is properly accredited and meeting standards.

"What would make this tragedy worse would be to assume this ("re-homing") is commonplace in adoption," he said.

"These tragedies are quite rare. We need to continue, though, to improve this process and afford families and children greater protection."