What would you call this smile? [closed]

Let's say that you catch your child eating a box of cookies alone. You scold him and forbid him from eating it as it is not for him to eat alone. Later, when the child is playing with his younger sibling, he realises the loophole. You forbade him from eating alone but he can have it with someone else.

Charlie saw a _______ smile spread on Devon's face as he looked at his sibling.

I am looking for a word to fill that blank. I am looking for something which would mean cunning or scheming, but not those words as they make it seem like an adult doing something nefarious. This is just an innocent child who has figured out a loophole to his advantage. There is no evil intent here. Do note that since this is in third person, so Charlie does not know what Devon is thinking only that something fishy is up.


Sly: having or showing a cunning and deceitful nature.


  • Charlie saw a knowing smile spread on Devon's face as he looked at his sibling.

From AHD:

knowing: ...

  1. Showing clever awareness and resourcefulness; shrewd and worldly: Even so knowing a young ruffian as William Chaloner would have had no preparation for the shock of London (Thomas Levenson).
  2. Suggestive of secret or private knowledge: a knowing glance [/smile, Lexico]

a smug smile/grin

Smug

Cambridge online

too pleased or satisfied about something you have achieved or something you know:

Also: a smug grin

Grin actually refers to:

smile broadly, especially in an unrestrained manner and with the mouth open.

Cambridge

Charlie saw a smug grin/smile spread across Devon's face as he looked at his sibling

However, I am suggesting... :

smirk

a smile that expresses satisfaction or pleasure about having done something or knowing something that is not known by someone else:

-Cambridge online

Charlie saw a smirk spread across Devon's face as he looked at his sibling

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This is non-judgemental, and seems to suit a child's viewpoint. It's like a repressed "yenh, yenh".