I created the filters you suggested and it returned both the person and that person’s children. It did not return just the children. Then I expanded the Filter1 flexibility and re-named it SpecificPeople.
The added flexibility was to set up SpecificPeople to look for a list of IDs in the example.gramps tree. (Please use this example tree when asking questions about building a Custom Filter. It lets us reproduce each others results and eliminates having malformed tree data causing issues.)
Usually, I set something like the SpecificPeople to look for people with a “Tag”. Then I do not have to remember the RegEx (Regular Expressions) pattern matching format. (And so I can quickly re-target the filter and see the targeted people with the Tag color.) But in this case, I used the Clipboard context menu to “Create Filter from the person selected…” as a shortcut.