When my DD was similar age she started to become more interested in why BPs couldn’t look after her. Very much felt it must be because she was a ‘bad baby’. We’ve had support from ASF to help her understand, process and cope with all she’s been through, which has helped and continues to help.
My narrative to her has been along the lines of ‘BM couldn’t keep you safe, that’s why the wise judge / social workers (delete as applicable) needed to find a new family for you’. I give her lots of verbal and physical reassurance that I’m her mum forever, that there’s nothing that would ever make me not love her etc, that she’s safe with me.
In our situation (and appreciate yours may / will be different) I’ve framed that reassurance and narrative alongside ‘when you are an adult I will help you to make contact with BPs if you want to, in a way that will keep you safe’
It’s really tough, and I don’t have a magic answer but keeping the line of communication open between you, alongside reassurance that nothing that happened to them was their fault, and that you are here for them forever is key I think.
I’ve got another thread going about self harm because that’s where things have got to for my DD at moment, but I do believe that being open with her from a young age has been helpful (and will be helpful long term) even if it doesn’t feel like that right now!