There are a number of untranslated "buts" or "howevers" in the Greek verse that are left out of translation. Since this word indicates opposition, their existence indicates that each of these lines was spoken as part of an unrecorded dialogue where Jesus was objecting to what was said (Unrecorded Dialogue).

This explanation of the "seed" as the "children of the kingdom" expands on his earlier explanation of the Parable of the Sower where the "good seeds" were the  ones understanding and using the news of the kingdom.  If the message was not received, the seed would not have been "good" or "beautiful"  (see this article on the Parable of the Sower and Information Theory). These equating of "seeds" and "children" is less obscure in Greek than they seem in English because the Greek word "seed" is a common word used to refer to "offspring."