Oh really?
The only conclusion supported by the data is that the threat of severe weather alleviates traffic. Pinning it on kids, just because most of the people the author knows still went to work, is nonsense.
I'd assume this article was satire, but it's written with such sincerity that I don't think it is.
I don't have real-time flow of all data, thus I could be completely wrong. All I have for traffic data is a few Google traffic maps.
On a somewhat different note, it may not be the same there, but around here (Fairfax County, near DC), school opening times are staggered fairly substantially in order to make better use of the bus fleet. Schools here start anywhere from 7:10AM to 9:20AM. This will also spread out car traffic, not that the school district does that intentionally.
I live in a southern city that occasionally gets ice, vast majority of people take that opportunity to just stay home. Nobody in the south can drive in ice. When that happens. Traffic is light whether school is in session or not. Therefore, I say kids have zero impact on traffic. Ha!