How do you know when you are a tween? It's an age thing and an attitude thing. If you are acting like an adult, and then a kid, does that make you a tween? You know you're a tween when you start hanging with friends, not having playdates. When you're staying up past your annoying bedtime, you know you're growing up. When you start going to parks just for a place other than home, and you go to stores with your own money, you're a tween. The downside of being a tween is you often have homework on the weekend.