as for the DF-02 yea a 6yo could handle it I let my nephew drive mine a few times when he was 5. It is brushed so it goes maybe 19-24kph so its not very fast... but can be made to go over triple that speed as the one I use has been shown(note the one I use has a lot of upgrades done that cost more then the RC's kit did )

As for the one mod I would do out of the box here are instructions http://www.rcuniverse.com/forum/rc-e...m-chassis.html
It took me maybe 10 minutes to do 3 DF-02s (I own 2, and my older nephew has one)
I will say without that modification the thing does have a tendency to rip like the 1st pic in the thread shows why Tamiya didn't do such a simple fix, or even sell it as an option is beyond me.
My nephews bone stock XB DF-02 hasn't broken a chassis since I did the mod 4 or so years ago