Just as brown11b mentioned kids 10 and Under are free at Lincoln Park Speedway. Maybe they could offer a discounted ticket for kids between the ages of 10 to 16 for their regular shows.

You mention "kids under 16 years old would be free as these kids will eat more food than it costs to get in for $20". You are allowed to bring a small cooler in with no alcohol. So that can destroy your theory right there.