We have all said the same, parables have a single message.
I am a children's teacher, so I will put it as I would for them:
God knows who are His and who are not. Even though while we are here on earth, the people of the world intermingle with God's children, when it comes time for God to gather His family together, those who are false will be separated out and judged, while those who are His will be gathered to be with Him eternally.
Now chette has already pointed out that the Scriptures answer most of my questions in the verses following the parable. Parallel verses in other areas also aid in interpretation (authoritatively I might add
). Where things get fuzzy is if one tries to interpret every detail of the story beyond the point of the message. Example: The good seed is the children of the kingdom, the bad seed are the children of the wicked one. Does this mean that a bad seed cannot become a good seed. Is this evidence of the hyper-calvinist definition of election? AND, who are the sleeping men?