Whenever possible English squeezes in a possesive pronoun. Czech does not like to do it unless comletely necessary. If the father in this sentence was not his, czech would say "some" or "somebody's" or something like that.
Where in the Czech text is HIS hidden? I am with LeinadSpoon on this one.
I'm pretty annoyed that this marked it wrong when i said boy's instead of boy is. It's a contraction!
Contractions are handled by Duolingo centrally, you can complain in the Troubleshooting section of the discussion.