Found out myself fairly early in my childhood. My parents were never that great at hiding anything, so that's how I figured it out. I never told anyone since it never mattered much to me. Regardless, that secret never broke the spirit of Christmas.
I was never really told about them being real or not real. My dad did try to make me believe in "Moses Clause" as a kid but I didn't believe him [I'm from a Jewish background, so I only celebrated Hannukah normally- but since 99% of my classmates celebrated Christmas, dad used to use weird things like getting a tiny tree and calling it our 'Hannukah Bush' and telling me about 'Moses Clause' to make me feel less left out].
As for the Easter Bunny...I never believed it no matter how hard people tried. I used to go to my godmother's house for Easter [and even other similar holidays] and my godfather would change out the eggs I painted with her overnight. He'd claim it was the Easter Bunny- but I had a hard time sleeping, so I sometimes saw him sneaking around at night and pieced two and two together. He was sad when I wouldn't believe him. Then again...He loved trying to make me believe in magical stuff. He used to say he had purple eyes. I got mad for his lying.
I was probably 13 or so when I actually stopped. My parents did an awesome job hiding things (to this day I still don't know where everything was hidden). I never really cared whether or not he was real, though. Free stuff was always good. :D
I believed in those things when I was in grade school. I can't remember how I came to find out they weren't real though. I don't remember if someone eventually told me or if I eventually figured it out for myself.