Posting this on behalf of my niece.
She always thought her step-dad adopted her after her mum died (we as a family supported this as it meant she could stay with her siblings) - we also believed she was adopted too.
Now she's over 16 she's moved in with her bio family. Her dad is now 'struggling' now he's £700 down a month for her. He said he didn't do it for the money but it definitely 'helped'.
No authorities have been in contact with us now she's living with us.
Does this mean she's been fostered all these years as surely if she was adopted she wouldn't of had that kind of financial help from the government?