pon-pon
A light, bouncy tapping or popping sound — patting someone on the back, tapping a drum lightly, or corks popping out of bottles in succession.
💡Patting a child's head — 'The teacher patted her head pon-pon.'
子供の頭をぽんぽんと叩いた。
I patted the child's head pon-pon.
She gently ___ tapped his shoulder to comfort him.
慰めるように肩を○○と叩いた。