expression
children pay back their debt to their parents in full by age 3 (through their cuteness)
Proverb expressing that a child's adorable behavior up to age 3 is so precious it repays all the care they receive.
「子供は３歳までに一生分の親孝行をする」と言われるように、幼い子の笑顔は何よりの贈り物だ。
As the saying goes, 'A child repays a lifetime of filial piety by age three,' and a young child's smile is the greatest gift.
A modern Japanese proverb; the exact origin is uncertain, but it reflects a common cultural sentiment about the joy small children bring.