I'm kind of late to the party, but I could see it working if they tweaked the format a little bit.
Instead of four-player teams, keep it to two-player. And while I liked the idea of the younger kids racing, perhaps the age limit could still be lowered. Not to pre-teen years, but 16/17 at the least. That way they could still do some of the challenges and could do a little more. It seemed as though the later challenges in the season weren't child-friendly.
And make it so that they go around the world, too. Other than that... Summer filming.