I came across this article from the Wall Street Journal and it has some really good research. Below are the stats: 
From 2000 to 2009, the latest year for which figures are available, the number of kids aged 7 to 17 playing baseball fell 24%, according to the National Sporting Goods Association, an industry trade group. Despite growing concerns about the long-term effects of concussions, participation in youth tackle football has soared 21% over the same time span, while ice hockey jumped 38%. The Sporting Goods Manufacturing Association, another industry trade group, said baseball participation fell 12.7% for the overall population.
As for Little League, which covers kids aged 4 to 18, about two million kids played in the U.S. last year, compared to about 2.5 million in 1996—an overall decline of 25%. The only growth in youth baseball participation since the 1990s, according to the NSGA, has come from kids who play more than 50 times a year—which suggests more children who play baseball have chosen to specialize.
Studies suggest more people now play soccer in the U.S. than baseball, and lacrosse participation among kids has more than doubled in the last decade. The number of high school lacrosse programs has been growing by about 7% a year.
