C.,
Let the boys see what Santa left, then have a discussion with them if necessary. I trust that they will like the other items Santa chose to leave them, since you and Santa are probably pretty close on the boys' desires. They may not be too disappointed with their gifts.
It's never too early to learn that you don't always get what you want, even from the Big Guy. You can perhaps let them know that Santa thought that they were a bit too young to have these motorized vehicles. If you don't mind them eventually having these, let them know that when they are 10 years old, or when they keep their room clean, or whatever, then maybe Santa will know that they are ready. That way, you have a way to help guide them.
Best of luck.