You would get made fun of if you have siblings, trust me, I was a brony in February 2012, and my older brother made me realize bronies are loving weirdoes. But it's entirely up to you, if you know your family won't make fun of you, go right ahead.
Regardless, they will find out some time or another, but seriously, I had no problems telling my family I was a brony, it's not like you're coming out of the closet.