can you see the future? you say it isn't happening and will not happen. how can you be so sure?

Because it is my field. I am a public health researcher and medical professional and I can tell you that you are talking the most unmitigated balls, fabrications and bullshit. Sorry.

in addition, how is a child who isn't vaccinated a threat to a child who has been?

Because immunizations aren't one hundred percent effective. Everyone's immune system is different. Sometimes people who are immunized don't mount a typical immune response and develop the necessary antibodies that prevent a certain disease. That's why we need widespread coverage, and why unvaccinated children are still a danger to the vaccinated. This is stated clearly in the article you provided.

in the article i linked, the doctor talks about how some people who have been vaccinated can shed the vaccine and in a few cases have been proven to infect those most at risk.

Vaccine shedding being widely dangerous is a myth perpetuated largely by anti-vaccination idiots who read a scary headline. The fact that disease transmission via vaccine shedding is incredibly rare is a meta refutation of this point. I'm going to quote directly from this excellent summation of actual, real data, which uses peer-reviewed research to debunk this concern:

• Viral shedding applies only to live virus vaccines and is significantly low, low risk
• Post vaccination viral shedding of rotavirus and varicella is detected in the stools for 4-6 weeks respectively. It’s of such low risk as to be of cautionary interest regarding immunocompromised individuals
• Genuine concern about viral shedding in these groups is managed with sound hygiene and avoiding contact with stools
• In rare cases of post varicella immunisation vesicular rash shedding may occur. Transmission is still unlikely
• The lack of viral shedding following MMR eliminates any concerns about transmission
• Claims of DTaP shedding and transmission are bogus
• Stories about whooping cough transmission from vaccine shedding are demonstrably false
• Antivaccination lobbyists use false and incomplete information about shedding to create fear of vaccines/the vaccinated
• Shedding of LAIV is at markedly low concentration, short duration and transmission is dwarfed by seasonal influenza transmission
• Accurate information about the topic is drowned out by antivaccination sites and “mothering” forums making inaccurate claims

if we are going to deny the unvaccinated access to school because of the danger they pose, what about these vaccinated kids?

Because in a straight up risk assessment, the chance of a vaccinated kid infecting another vaccinated kid (or even an immunocomprised, unvaccinated kid) are so miniscule as to be nearly statistically insignificant. Conversely, the chance of an unvaccinated kid contracting something and spreading it around is much higher and in fact that situation has precipitated several outbreaks.