Most people can't deal with the level of sacrifice it takes to be successful. Sometimes it takes the entire family to sacrifice and that just isn't an option for most people.
Carl Edwards wanted to be a race car driver real bad. He drove himself to the track in his van (which he slept in) and only had a handful of shirts/pants at any giving time.
My chassis set-up guy in Indiana said Carl would call & stop by his shop to shower and sleep on an actual bed a few times a month. He did that for several years before picking up that first NASCAR truck ride part time.
UNOH is very involved in motorsports. It's a great place to go if you want to play with cars for a living. If your kids go to college and get a degree, it does not have to curb their racing career, ask Ryan Newman.
http://www.unoh.edu/academics/college-of-applied-technologies/high-performance-motorsports.shtml
Beyond that, put together a resume of their racing accomplishments to date, including pictures and their schedule for the following year, then send it to everyone you can think of that may give them a few bucks for racing. I'd start by sending it to everyone you see sponsoring anything in motorsports. Don't forget local buisinesses too. I heard a story about Carl Edwards as a kid, 14 or 15, had business cards and he'd hand them out to anyone and everyone at the racetrack looking for a ride.