You inquired re:#1 also ... There are several ways to look at it. Let's start with the players.
The US child population is at or about 74 million. In 2012, there were 3 million youth players registered with US Youth Soccer. This 3 million figure has remained unchanged during the past decade. It constitutes only about 4% of the child population. Within this, certain segments of society are glaringly under-represented.
The numbers peaked in 2007/2008, but are now back at year 2000 levels. It's a drop in the order of about 100,000 players, and is likely attributable to economic considerations.
Other kids participate outside of the 3 million.
1974 - 103,432
1980 - 810,793
1985 - 1,210,408
1990 - 1,615,041
1995 - 2,388,719
2000 - 3,020,442
2005 - 3,050,465
2007 - 3,123,698
2008 - 3,148,114
2009 - 3,094,868
2010 - 3,036,438
2011 - 3,025,551
2012 - 3,020,633