Proverb meaning that you can judge a parent by observing their child, as children often reflect their parents' traits.
Seeing that child's politeness, it's a case of 'like father, like son.'
親見たけりゃ子を見ろというから、彼の両親もきっと立派な人だろう。
They say 'like father, like son,' so his parents must be fine people too.
A Japanese proverb composed of 親 (parent), 見たけりゃ (if you want to see), 子 (child), and を見ろ (look at). The exact origin is uncertain, but it reflects a common folk observation.