How do i tell my parents about my girlfriend?

alright , well i have 2 quistons so read it all..i had a girlfriend for about 2 days now but my parents dont know yet. im 12 and ive had other girlfriends and it usually just comes up. last time my sister just sprayed it out there and im like oh yea sorry i forgot to tell u. usually the will make it a big deal and be like ooo shawn has a girlfriend. im afraid of that happening. my sister knows but she will probbaly tell my parents when she gets the chance or idk what she will do. my sister will be more embaring but better in some way. my parents r usually happy but its a big hle for them to ... lets say im sad cuz i did something my mom would be like go tell your girlfriend about it... another thing is bicly why i wanted to ask this quiston is on Facebook. my girlfriend isn't putting up shes in a relationship. cud she be in the same situation. cuz my sister is in college so she dosnt have much contact with my parents other than txts and calls. hr sister is in highschool. she isnt putting it up... i usually do tho. her friends no about it but none of mine do what shud i do. and how can i make my girl happy she gose to a diffrent school we text and stuff but her stupid friends usually get in the way of it.