if you know that her bf was the father, why don't you just say there was mummy called T and a daddy called D and they had a baby called K.? Then write things that you know or believe to be true eg
"they loved baby k very much and were very happy when he was born. but they had a lot of problems and were not very good at looking after a small baby. they didnt feed him properly or change and bathe him . sometimes they went out and left the baby at home by himself. they had so many problems they couldn't even look after themselves , let alone a small baby
so the people in charge ( social workers, courts) decided that they had to find a new family who were able to look aftre baby K . T and D were very sad and angry as they wanted to keep baby K but it wasn't safe and he could have got really sick or even died
so baby K went to live with M&J, who looked after him until the social workers could find a forever mummy and daddy for him. then they found X and Y and baby k went to live with them and now they are his forever mummy and daddy"
then you can write about how happy you were when he arrived, how you prepared for him and welcomed him, what family members did / said/ gave him etc
obviously it depends on the age of your child. but please don't say things that are not true and then retract them when he is older
eg they placed the child voluntarily for adoption if he was in fact removed
or the child was removed because they were too young or too poor. because that's not true. and also your child may worry that if you are short of money he will be taken away again
i think its important for children to know that babies and children are not taken away for minor reasons, it has to be extremely serious. otherwise they coudl feel even more insecure through out their childrhood
soem of the adoption life story type books are very dated and assume that all babies were relinquished. and also that its easier for the child to believe that he/she was given away, rather than removed by the authorities. goodness knows why................ i suspect because its easier for the adults that way
HTH