Perhaps it is some kind of moral message, about what a kid
should
want as a gift or reward. Riding a bike is more healthy than playing Xbox, but which one does the average kid desires the most these days? Not sure if that was the intention, but I think it's not bad since it's a family movie to watch with your kids.

That seems like a gross after the fact fix to bad script writing. "We couldn't replace the cheapo bikes with expensive ones". Right. It would literally take an hour or two to find and buy 2 expensive kid bikes. And even then, really expensive kid bikes would be a few thousand total. If they don't have a few thousand put away some where they have no business having kids.

oh, lol.
But even that doesn't make sense. Look at those two kids. They aren't the mountain or race biking sort.
Lisa needs braces. Dental Plan!
Pyle! Shazaam!
Can't sleep. Clown'll eat me.

And even so, that's precisely the thing. He's too busy chasing a raise, a promotion, the dollar sign, he thinks that makes him a good dad being able to buy them things, not spending time with his kids like he should've.

If you listen to the audio commentary, the bikes were supposed to be very expensive reacing or mountain bikes, they bought the wrong props and didn't have time to replace them beofre shooting.

I was trying to be generous so that no one would come in and say "wtf, those bikes were wayyyy more expensive."
Lisa needs braces. Dental Plan!
Pyle! Shazaam!
Can't sleep. Clown'll eat me.

What? Where do you live that two bikes like those cost $500!? I wouldn't pay more that $130 for both of those