This is the 7808th most frequent Polish word.
małoletni
"Małoletni" means "minor" or "underage" in English.
In this sentence, 'małoletni' refers to individuals who are under the legal age, and the usage is general as a noun.
Małoletni nie mogą prowadzić pojazdów mechanicznych.
Minors cannot drive mechanical vehicles.
Here, 'małoletnich' is used in the genitive plural form as an adjective/state descriptor referring to minor-aged individuals.
Zatrudnienie małoletnich w tej branży jest zabronione.
The employment of minors in this industry is prohibited.
In this context, 'małoletni' serves as an adjective describing 'pupils' as being underage.