Through the years, Hot Wheels cars have been collected mostly by children. However, since the late 1990s, there has been an increase in the number of adult collectors. Mattel estimates that 41 million children grew up playing with the toys, the average collector has over 1,550 cars, and children between the ages of 5 and 15 have an average of 41 cars. Most believe the collecting craze started with the Treasure Hunts in 1995. Mike Strauss has been called the father of Hot Wheels collecting; he has organized two collectors' events each year in some form since 1986. The first event was the Annual Hot Wheels Collectors Convention, normally held each year in the fall. The convention occurred in various locations around the country until 2001, when the first Annual Hot Wheels Collectors Nationals was put together. Since then, the Conventions are held each year in southern California. The Hot Wheels Collectors Nationals rotate among cities outside of California during the spring.