Sounds like a total fuckup on the part of the police.
BBC link says the granmother reckons someone overheard the police make the phone call. The person who collected the child was not asked for ID, they did not get the mother to check she was the right person, she was totally the wrong age (nearly 20 years younger than the real person) and SHE GAVE THE WRONG ADDRESS. Yet the coppers handed the child over.
When the mistake came to light they went out and arrested all of the woman's family even though they had nothing to do with it. Not questioned, arrested.
FFS.