Even though your child was born mid-year, you are allowed to indicate that they have lived with you for the entire year. If the partial year selection has been carrying forward each year and is the reason why your credits were reduced, I would recommend seeing if amending your returns might be beneficial (you have 3 years from the date you filed your original tax return or within two years of the date you paid the tax, whichever is later). It's hard to know if it will have any impact without seeing all of the information, but it might be worth looking into.
