You can get the child tax credit for a child who was born on 12-31-2024 up to age 16. If the child turned 17 during 2024 you lose the child tax credit. If you are not getting the CTC for a 3 year old then you must have answered something incorrectly in MY INFO.
Make sure you have entered your child as a dependent in My Info, and that you have entered the child's Social Security number.
Careful— do not say that your child’s SSN is not valid for employment.
If your child was born in 2024 make sure you said he lived with you the whole year.
There is an oddly worded question that asks if the child paid over half their own support. Say NO to that question.