Moding a Walmart "ride-on"?? (battery powered trucks for little kids)

Hi! New here. Guy on the UE boards sent me over here.
Heres my question.

My little brother and sister both have little trucks kind of like this one.



http://www.walmart.com/catalog/produ...%3A4198%3A5353

They never play with them anymore, so I was thinking of trying to mod one. I'm really not sure what I could do to it, I haven't even really look it over yet. But I know I'd like to make it faster, but I don't know what kind of engine I could use, or battery.
I was thinking of maybe adding some rubber to the tires for better grip, but I think that would run the battery down real fast.
And I don't think I can make it much lighter.

Anyone have an Idea? I'm sure someone here knows something about electric motors.

Maybe once I do this they'll start using them again, They've been sitting for about a year.


Now. I've been told these use the same size motor as we use in RC. Could you tell me what would be a good size to use, or just what motor would do the job. and please give a link.

Is there anything else that I would need? other then the motor? like better batteries, or something?

Thanks.:D