Success! "It's all good" said my son.
I got my kids the first adult size bikes and they like them. Every time I got them new bikes as they grew I wanted them to like them and even more so now that these bikes may be sticking with them for more than 2 years.
most of their riding is on pavement now. when they were younger we took them camping and it was important for them to have wide manageable tires for the sandy campground roads. now that they are older they spend more time on paved bike trails and are more concerned with comfort; ease of use and efficiency. Each successive bigger bike got them closer to this goal.
Finally they both left mom and dad in the dust and wow what a jump in their average speed! I tagged behind to keep mom company (no kid of mine is gonna leave me in the dust, hahaha). So now Mom needs a better bike cuz she used to leave the kids in the dust, but now she can't keep up on the MTB. New tires for her old road bike or a new hybrid/straight bar road bike like my daughter's.
FYI: the bikes (Trek 700c hydrids) aren't brand new just new to us. As far as the kids are concerned they are a whole new ball game from the 24" MTBs we just got rid of.
Here's what they're riding now:
Trek 750 Multitrak (son has since raised his seat a decent amount)
Trek 7.1 FX