I have found a 6 year old child living with her "adoptive" parents in the 1921 census. She is enumerated as being the couple's daughter, with their surname but her middle name is the surname of her biological mother - could this indicate that the "adoptive" parents knew the biological mother of the child? or maybe there is another explanation?
Also, the child is enumerated as parents both alive. Would this mean that both the biological parents are alive or that both the "adoptive" parents are alive?
Margaret