Their EIC may have been denied. Also, sometimes people confuse the credits. The Child Tax Credit (which is not EIC) is not subject to the delay, but the Additional Child Tax Credit is.
Taxpayers will begin to see refunds claiming EITC/ACTC the week of Feb. 27. “Where’s My Refund?” will update for EITC/ACTC refunds beginning Feb. 16, with the vast majority updating by Feb. 18.
(You can always change your withholding so that you do not have to wait for a refund at tax time.)