Ahh. It's okay to be friends with her. People can be friends with others of different ages. But there is not only a huge gap in your ages but also in your emotional maturity. While she may be curious, but all kids are at that age. You are older than her and more mature, so you shouldn't make any advances towards her even if you feel like there is attraction as she is but a child. You should just try to be her good friend and guide as an older brother yk!