you'll have to wait to file the 2020 return. your spouse may have gotten the stimulus payments for the kids. Everything will need to be reconciled when you file the 2020 return. the actual Stimulus your family is due is based on the 2020 return. got too much you get to keep it too little and you'll get an additional refund.
The stimulus checks being sent out this year are based on 2018 or 2019 tax returns. There is not a way to add a dependent you did not have in 2018 or 2019 to it this year to get the money in 2020. As HACKITOFF said, you have to wait for your 2020 return that you will file in 2021.