Important things about Big Wheels.
First of all, they are awesome and may lead to a life long fascination with all things wheeled.
If you get it going really fast on any hard surface, stopping the pedals just means the front wheel slides, like flat spotting in F1, kinda.
If you have crazy relatives, and I mean crazy, and they allow you to ride one down (or partially down) a hill used by motorcross bikes, do not keep your feet near the peddles. Keep them splayed out for balance. Once those things get going, they are will grind anything that comes in contact with them.
Finally, they are awesome, I often wished for an adult sized one, then saw a recumbent bike and said, nevermind.