Hello, Is there a Netsuite functionality that will allow us to close the child WO's when I close a Parent WO's?

No there is not any native way to accomplish this. If I may ask how many Users currently have access to closing Work Orders? Normally I would recommend 1 to 2 Users in a mgmt or supervisor Production role to be closing the Work Orders. If you add the Item Type onto the WO transaction form it makes it pretty clear which lines belong to a Sub-Assembly Work Order. I normally see a bigger issue when Sales Order lines are closed that have Special Work Orders linked to them and they remain open. I have designed a solution for that with a couple different clients.

Thanks a lot for the info.