This is something I debated for months before ultimately deciding to let my mom in on it, mainly because I still live with her for financial reasons and felt it was the best way to prevent any sort of accidental discovery. To minimize the chance of a negative reaction, I spent quite some time figuring out which details were necessary to discuss, how to explain it in the least awkward way possible, and why it was something important to me. The result was a 90 minute conversation about ABDL and babyfur stuff, with the outcome that as long as I didn't try to force anything on her and didn't attempt anything dangerous she was totally cool with pretty much all of it. It actually ended up being way more positive than I anticipated, and it's allowed me to be a lot less self-conscious about the whole thing. Naturally, I'm not going to go around telling people if they don't need to know, but it's not something I'm going to stress over concealing at all costs.
If you're thinking about telling parents, my advice would be to first think carefully about what is to be gained by both parties through the knowledge. If there is not a mutual benefit, it is probably not worth bringing it up. Once you've determined it will be a good thing, do plenty of research to figure out exactly what and how much you want to reveal, as well as to figure out the best way to approach the subject based on how open your parents are to unusual ideas. Be completely honest with what you do tell them, but don't feel that you need to go into extreme detail about the topic. Keep the focus on you and why it is important to you, not on what the particular interest is. That said, be prepared to answer any questions they may have. Lastly (and perhaps most importantly), do not try any of this if you haven't already accepted it yourself. You need to be confident about this side of yourself, and you need to present it in a positive light. The weirder and more awkward it is to you, the harder it's going to be to convince someone else it is perfectly okay.
