Qualifying dependents are those you were allowed to claim for a tax credit in box 4 of federal form 1040 (IRC §24).
2a. Enter on line 2a the number of qualifying dependents age 16 or younger on Dec. 31, 2018.
2b. Enter on line 2b the number of other persons not included in 2a for whom you were able to claim a dependent tax credit. You may not claim yourself or your spouse as other dependents.
2c. Add lines 2a and 2b and enter the total on line 2c.