Matt,
I took my son to the track when he was about that age. I would just suggest that they obviously try to avoid any super loud cars, but from what I understand Gulick won't be there with his RX7. Some type of ear protection is a good idea, although we didn't use it (had it with us though). Worst case, they can go to the outfield grandstands with the baby for a bit where's it's a little more quiet.