I would just use Child. Once the adoption is final they are legally your child. I have no idea why that choice is even there, except for one that is not yet final. From the 1040 instructions
"Adopted child.
An adopted child is always treated as your own child. An adopted child includes a child lawfully placed with you for legal adoption."

I think "Adopted Child" on the tax return refers to that you are using an ATIN, rather than a SSN.