She has a roguish smile!

The noun form for the adjective roguish is roguishness. Another noun form is rogue.

Roguish has two very different meanings, depending on whether the rogue involved is considered a villain or simply a similarly colorful character.

Roguish :

1) Unprincipled or devious (roguish band of thugs)

2) Playfully mischievous (a roguish grin)

The question should be: What are children WHO are mischievous or roguish called? 'That' refers to inanimate objects.