What form do you need to attach birth certificate

What?   Where are you seeing anything that is asking you to do that?

You don't normally attach anything to you tax return, even when paper filing .  What are you trying to accomplish? 

My DocsTM is available in all paid TurboTax Online products or by adding PLUS to Free Edition. Sign in to your TurboTax account.

1. If you're already signed in,
2. select Tax Home on the left menu
3. Scroll down to Your tax returns & documents.
4. Select Show and select your desired tax year
5. Select My Docs to elect Upload and select the document you want to upload Answer the questions and
6. select Done or Upload another tax form  

My DocsTM is available in all paid TurboTax Online products or by adding PLUS to Free Edition.

1. Sign in to your TurboTax account. 
2. Scroll down to Your tax returns & documents. 
3. Select My Docs.
4. Select Upload and select the document you want to upload.
5. Answer the questions and select Done or Upload another tax form.