Widget Visibility: "children" rule disappears when adding additional rule

### Impacted plugin

Jetpack

### Steps to Reproduce

1. Go to Pages > Add New and publish a new page
2. Go to Pages > Add New and publish another page, this time marked as child of the first one using the options in the editor's right sidebar.
3. Go to Jetpack > Settings and enable Widget Visibility
4. Go to Appearance > customize and add a legacy widget
5. You'll see a "Visibility" button appear below the legacy widget: click it
5. Add a Page visibility rule, and check the box to include children.
6. Now hit the "+" icon to add an extra visibility rule.
7. Add that rule and save your changes
8. Upon refreshing the page, you'll notice the "Include children" checkbox is no longer checked.

### Other information

Reported here:
https://wordpress.org/support/topic/visibility-include-children-issue/

Reproduce the issue through Jetpack > Settings and Appearance > Customize using the legacy widget and the Page visibility rules described. Trace how the Include children selection is persisted when a second rule is added, then verify after saving and refreshing that the checkbox remains selected.

Written by the indexing model from the issue text.