I want to tell my biological son that I don't want a relationship with him
Do you really want to reject your son?
Yes, I am tired of him.
It is wrong to reject your children. You can cause them a lot of psychological harm knowing you reject them as a person.
I'll handle it.
Please try to keep in touch with your kids. If they are really young they don't understand what is going on. He may internalize it and go down a bad life path.