Parents asked me if I'm having sex with my boy

I'm 19 years old about to be a sophomore in college. My parents are pretty good about leaving my personal life alone and don't usually ask a lot of questions but recently I told them I'm talking to/dating a boy I used to be involved with in high school. The first time we had sex was over a year ago and we've kind of been doing it ever since but for the last 9 months or so we've re started a relationship with each other and consider ourselves to be dating. The other day my mom asked me straight up are you guys having sex and I didn't really know what to say because I obviously don't want to tell them I'm having sex but I'm also 19 and an adult and they shouldn't be getting mad at that. Do I bring it up and admit the truth or wait til she brings it up again or just deny it again because it's none of her business at the end of the day. I especially don't want my dad to know I am because I feel like he will look at me differently and both my parents waited til their 20s to have sex. Thoughts???