Otokonoko (男の子) means "boy." This word specifically refers to a male child. It's a combination of "otoko" (man/male) and "ko" (child), clearly indicating a young person of the male gender. You would use it when talking about young males. Example: あそこに男の子がいます。(Asoko ni otoko no ko ga imasu.) = There is a boy over there.

子(こ)供(ども)の男(だん)性(せい)を指(さ)す言(こと)葉(ば)です。「男(おとこ)」と「子(こ)」でできています。例(れい)：あそこに男(おとこ)の子(こ)がいます。