I've recently found out that you can serialize items if it's new only using

<evaluator type="Unicorn.Evaluators.NewItemOnlyEvaluator, Unicorn" singleInstance="true"/>

When I add this to the configuration, all the items I include will only be serialized if it is new.

I would like to serialize a parent item and only some of it's child item to be serialized when it's new. How can I achieve this?