How about not threatening to make a fire break out?
Ryuutaro sighed a bit. Somewhere between cute and a danger to humanity, that described Hayato in combination with the kitchen very well.
Ryuutaro decided it would be best not to leave Hayato anywhere close to the deep fryer and instead let him spent time with the rice, which was just finished cooking.

"It'd be nice if you could split up the rice between two plates, alright?"

... he could do nothing wrong here, even if he started counting the single pieces.