Use case

The Checkbox and Radio widget have fixed sizes that might be too small in some cases, also depending on the overall UI design. An UI with usual icon buttons of the standard size might want to use the same size for these controls as well, especially if they appear near to each other.

Proposal

The suggestion is to add a scale variable to both CheckboxThemeData and RadioThemeData and pass them through to the actual widgets. Individual checkboxes can be manually scaled as:

Transform.scale(scale: 2, child: Checkbox() ...

but this won't help CheckboxListTile where the size remains the same. Changing the underlying widget to use this scaling approach would solve that, too.