Fix nth children in loops

[UnnaturalTwilight]

Description

Fixes children of custom widgets that use the nth property never appearing if the custom widget is placed in a for loop.

Checklist

Please make sure you can check all the boxes that apply to this PR.

• All widgets I've added are correctly documented.
• I added my changes to CHANGELOG.md, if appropriate.
• The documentation in the docs/content/main directory has been adjusted to reflect my changes.
• I used cargo fmt to automatically format all code before committing