childishness russian

• мальчи́шество

  boyishness, boyish immaturity, youthful recklessness

  boyish prank, childish trick, childishness

• ребя́чество

  childishness

Examples

• Хватит мальчишества, тебе уже тридцать лет!

  Enough of this childishness—you’re thirty already!