Kids can not only walk, but walk alone too. I was going to elementary school on my own when I was 7. So did my classmates. I used to cycle all around by the age of 10.
It sucks that today youngsters are treated as dumb. Even though the world is getting safer and safer.
That would be ca. 30 minutes cycling one direction, then another 20 minutes to the train station where I need to catch my train. 50% of the route on country roads where overtaking trucks are great funs. With a lot of rainy days from October till April and a few days of snow in winter months.
So no, I did not consider biking with a second seat. It is completely unrealistic.