As a short-term work-around to allow more information about dependent ages to be used in taxsim9 it is allowed to specify item #19 (depchild) with an overloaded variable that includes 3 age categories. The overloaded variable is calculated as the number of dependents under age 17 plus 100 times number of dependents under 18 (plus 10000 times number of dependents under 13. e.g. 10302 is 1 child eligible for child care credit, 2 eligible for child tax credit and 3 counted for EITC purposes. Note that the number under 18 includes all the children under 17 and under 13, and the number under 17 includes the children under 13.
It would probably be better for users of taxsim9 to switch to taxsim27 which does not overload variables and does a better job of calculating the NIIT.