I'm a father of a daughter. It's like this -- if I'm somewhere with my kid, and you talk exclusively to my child, and you don't make any eye contact with me or acknowledge that I am there, that is going to be weird. OTOH if you acknowledge me and say something like "She reminds me of my niece" or even just ask "how old is she?" then everything is fine. Kids at that age don't roam around the world alone -- they are with an adult. You need to acknowledge that I'm in charge of this situation, it's my kid. If you talk to or interact with a kid and don't acknowledge the parent, it's as if you are talking to some adult on the street, and that's weird and freaky.

In terms of "enjoying looking at her" I don't even know what to say, I mean if she does something cute or funny it's perfectly fine to smile or laugh, there's nothing wrong with that.

Do you have any experience interacting with nieces, nephews, younger cousins, etc? If you are worried about people perceiving you as creepy, go visit a relative and spend some time learning how to interact with kids. Once you get the hang of it, you'll feel more comfortable and less awkward. I think a lot of this is that men in our society aren't encouraged to learn how to interact with children, whereas teen girls are constantly being asked to babysit etc etc.

For my part, I never looked at kids or interacted with them until I became a father. Then I learned how awesome kids are and I have no problems interacting with kids even when I'm out by myself. There's a way to talk to them, there's a way to acknowledge the parent, it's all sort of intuitive, you need to get the hang of it.

Of course I am giving you the benefit of the doubt that you're not actually a pedophile and this post is not about your massively guilty conscience. But if that's the case then please ignore everything I said and stay far, far away.