Summing up child row cells to parent rows

Douglas Blake
edited 12/09/19 in Smartsheet Basics

I have reported production numbers and I have shipments going out. I want to take the production number and subtract it from the shipped # and give me a remaining QTY. When logistics moves more of the product they will add a row for the second shipment and make it the child to the first shipment. I would like the qty from the second shipment to be subtracted from the remaining qty in the first. Here is the formula i have so far and I'm getting an error. 

=SUM([Packed Out Retail Cases]3 - [Quantity Shipped 1]3)(SUMIF(CHILDREN([Quantity Shipped 1]4-[Remaining QTY]3)))

Any help would be greatly appreciated.