RE: Best choice for 6 year-old w/ newbie parents
The problem you have is that the pede will be a bit big for indoor use but a mini will not be good for outside in grass. The mini will do ok on pavement and dirt but grass will not be it's friend.
Personally, I think that the guys suggesting the pede have the right idea. It may be a bit big for indoors but not overly so. And as has been mentioned time nd again, it's a good durable truck with tons of parts available and one your son will be able to keep and grow into.
Hope you all enjoy the coming new toy.