Meaning of the Sanskrit Word: kumarasya

  kumarasya—of the newly born child    SB 6.14.35
  kumarasya—of the son born of Sakuntala    SB 9.20.18
  kumarasya—of boys like you    SB 4.8.27
  kumarasya—of his newly born son    SB 6.14.33

Can't find any compound Sanskrit words containing kumarasya.