I accidently forgot to check mark boxes 4a and b on my EIC form. Will that affect my refund? I've used the same dependants in the past.

It depends on the age of your dependents. If your dependents were born after 2003, boxes 4a and 4b are not required, and it will not affect your refund. 

Thank you! They were born in 2016 and 2019 so good!