Why am I being asked to add form 8839 "Adoptive child worksheet". I am claiming both of my biological children I don't see the form available to delete in "tax tool".

The information you entered somewhere may have triggered another form first.  Try looking for Adoptive Child Worksheet or Adoption Carryover Computation Wksht when you are viewing to delete a form.  To clarify how to delete a form you can follow these steps in TurboTax Online:

1. Within your return, click on Tax Tools in the black menu on the left side of the screen.
2. Click on Tools.
3. Click on Delete a Form. 
4. Scroll down to your form and click Delete.
5. Under Federal in the black menu bar click Wages & Income to get back into your tax returns.
6. Proceed entering/reviewing your return.