Help with acting please!?

i am 13 years old and i really want to start acting. i tried to hide the fact that i want to start to act because i am shy and everyone knows that. but now i just cant hide that i want to start. i started being more outgoing and not caring what people think. i finally told my parents i want to start acting and they think sure but this is just going to be a phase and dont get my hopes to high because they are just going to crumble down. they also said if i do want to start acting i should go in my school plays but they dont understand that people at my school go to the plays to laugh at kids they know. they dont believe me at all. how do i tell my parents that this is serious and this is what i want to do? and i live in florida and small auditions you guys know of ? this is serious because i beleive i can do this! please help! thanks