MarioKart for the Nintendo ds is one of the best racing games available for kids. There are over 30 courses to try out so you can be sure your kids won't get bored with it for quite some time. Of all of my daughter's Nintendo ds games, this one is her favorite. She loves when she does well and gets awarded a trophy.
I must admit that I have had fun playing this game too. It is rated E for everyone, but don't let it fool you. It is a little hard, and I think my daughter just might be better at it than I am.
To make things more interesting you can play this game with your friends. When you are in the same room you will be able to play together. You can also play with people all over the world. All you need is a Wi-Fi Connection.
So if you like racing games I recommend you get MarioKart.