Living aboard and do not have child social security number yet, do I still need to have the child in the tax return?

You do not have to include the child in your tax return, but you will likely pay more tax, or get a smaller refund, if you omit the child.

If you are a U.S. citizen or resident alien living abroad, you get an automatic 2-month extension of time to file your tax return and pay any tax that you owe. (But you will be charged interest if you don't pay by April 15.) You can request an automatic 6-month extension, which gives you another 4 months to file, but you must still pay any tax that you owe by the end of the 2-month extension.

CORRECTION: Because of the recently announced 90-day postponement of the payment deadline for 2020, you will not be charged interest as long as you pay by July 15, 2020.