I didn't view it as any of their business, but then I no longer live at home. If I did live at home however I still probably wouldn't of bothered telling them. I wouldn't have kept it a secret, but I wouldn't have made out it was anything special either since it's just another hobby and not really a gigantic lifestyle choice (insofar as it does not dominate all facets of my existence).
My mum always wanted me to be gay so I imagine she'd of been so pleased until I told her being a Brony had nothing to do with sexuality in the slightest and everything to do with appreciating good writing and enjoyable television. Then she'd of just not cared much either way.
I suppose the closest I've gotten to what you're asking is when my fiance and best friend figured it out (independantly of one another), my fiance thinks it's adorable and encourages it, my best friend screamed 'god why!' and pretended to choke me for about 3 minutes (for him, this is sadly fairly normal behaviour).
Don't worry too much about your parents reaction, as had been stated by these other fine folks it really isn't that big of a deal unless you make it one.