The Romantic ideal?
(Naku ko wa sodatsu; “The child who cries, grows”)
A baby that cries loud and often is a healthy one that will grow well. A strong cry is evidence of good health. Presumably this is a favored saying for new grandparents to quote to new parents.
We begin with the verb 泣く (naku), “to cry,” in prenominal form. This allows it to precede and modify the noun 子 (ko), “child,” in this case representing a baby. The particle は (wa) marks the crying baby as the topic of discussion, and the comment on this topic takes the form of the verb 育つ (sodatsu), “to be reared,” “to grow up,” in sentence-final form.
The theory goes that a baby who’s growing steadily will require a lot of food, and often. Add to this the fact that volume is an indicator of lung capacity and diaphragm power, or even itself a form of exercise, and it’s easy to see the folksy wisdom in this phrase.
…That said, if somebody blithely disregards your frustrations over a noisy baby by quoting this saying at you, feel free to respond with another one that goes 寝る子は育つ – replacing 泣く with neru, “to sleep.”
(“Naku ko wa sodatsu, tte? Dattara ore no ko wa kyojin ni naru darou.”)
[“‘Babies who cry grow well,’ eh? In that case my kid’ll be a giant!”]