I have to disagree to an extent. I'm empathetic to the birth "parents" to a point.
Why put parents in inverted commas? The child you have adopted has a biological family. This you knew before you adopted.
However, I absolutely categorically do not think that direct contact is in the best interest of a child (maybe very rare cases of older children being removed).
Why? Experts and more recently the UK government has said the exact opposite. Direct contact, is, where safe to do so, in the best interest of the child.
How can they ever feel like you are there real and only family if they are made to see their genetic family?
You are not and never will be their only family. You knew that when you adopted. Ties with biological family are vitally important.
Adopters are not baby sitters, they are a child's parents. Too many adopters make so much of adoption and cause issues. Children should just be your children (albeit, incidentally knowing thar someone else just happened to grow them)
No adopters are not babysitter's. You are their legal parents, but not their only parents or family. Again you knew this when you adopted.
Of course children should still be children. Letterbox or direct contact won't change that.
Interesting that you believe it's due to adopter's making too much of adoption that causes issues and not that the child most certainly will have some trauma and identity issues due to the being adopted and removed permanently from all biological kin. You do a great disservice to your adopted child/children by relegating their natural parents to mere vessels.
Your child's natural parents gave them life, their appearance, their genetic history etc,. Do not relegate them to being 'someone else who just happened to grow them'.
I sincerely hope that in a few years, attitude's like yours will become extinct as adopted people are given, in law more rights.
Imagine someone telling you that your bio family weren't your real family? You'd be outraged. Adoption doesn't change genetics or that reality. Then imagine, due to a contract, that permanently and legally removes you and all of your kin from being family. One that you cannot revoke in adulthood and if you chose to, return to your natural identity. Then you had someone, particularly someone like you, their legal parent, dismissing a huge part of who you are and their identify.
Disgusting stuff from you really with views that definitely belong in the past.