Go back to My Info and make sure you said your baby lived with you the WHOLE YEAR and not just the number of months. Even a baby was born on Dec 31 is considered to live with you the whole year. You might have to delete the baby and re add him. Pay attention to the questions, especially the one asking if he paid more than half of his support.
How old is your first child? They have to be under 17 on Dec 31, 2020. Your stimulus check is based on the number of qualifying people listed on your tax return for 2020. You don't receive a check for the new baby necessarily, it is just based on the number of qualifying people listed on your return.
So, if you lost one qualifying person because they turned 17 and replaced that person with a new baby, you still just have one qualifying person.
