Educate your parents about all the dirty facts you know about slaughter house. Show them all the videos posted on PETA site, that will change their perception definitely. They will be more considerate and respectful about the decision you have made for yourself. It helped me a lot in the initial stage when people used question my motive a lot but now all they have is respect and few have turned vegetarian too after talking to me.
My parents and family definitely weren’t happy or comfortable with my decision to be vegan but they knew I would refuse any animal products if they didn’t let me so I wouldn’t eat at all. But if your parents are really serious on not allowing you to be vegan then my best advice would be to convince them. Tell them why you want to be a vegan and just how important it is to you. Show them the abundance of food available for vegans that are healthy and give you all of your nutrients without harming animals. Maybe show them a video but just do your research show you can describe how being vegan is a healthy and ethical choice. If you show them everything and cover all the basics of what, why, and how then it might help persuade them. If you need any help, message me!