This is a particularly interesting story about a pair of foster parents and the foster children they looked after, back in the 1960s and 1970s. They had up to 11 children living with them at any one time! There are many things that seem to have changed about fostering since those days, and I'm pretty sure that the number of children they could look after at once is one of them.
The book particularly features a brother and sister who came to them at age 1 and 2 years and remained with them for the next ten years, during which time he children were mostly pretty happy. Sadly this came to an end when social services decided to reunite the children with the mother who had abandoned them when he boy was born - an arrangement which lasted all of two weeks. :-( Trisha Merry did not find out what had happened to the children till many years later, when one of the children managed to contact her.
At the time the Merrys were fostering, social services didn't usually tell foster parents anything at all about the background of the children they were fostering, which seems to me incredibly short-sighted. I know there are still problems in this area, but I think it has improved.