did something dumb at 13. not sure how to move forward

When I was around 13, I did something that I deeply regret and I’m unsure how to feel about it. I jokingly asked my brother(i think he was 8) to kiss me (I know it was stupid and immature), and after hesitating, he did it. I didn’t physically force him, but I think he agreed because I told him I’d let him sit where I was sitting if he did it. Looking back, I realize how inappropriate it was, and I wasn’t thinking about boundaries at the time. Now I feel ashamed and am wondering if it was just stupid kid shit or if it could be considered something more serious like sexual assault. I’ve been reflecting on it a lot and feel conflicted, so I’m looking for some perspective—was this a common mistake made by kids, or did I cross a serious line?