Will you be my friend?

I just love the innocence of children. How they're not afraid to make new friends. They don't worry if they say the right thing or not. They have no expectations only to just play, and be friends, in the moment.
I took Cammy to the park today and while I was throwing the ball to our dog, Cammy goes off to play at the play structure. There's kids all over, playing in their little groups that they came with and then there's Cammy. What does she do? She starts playing with a little group of kids and makes friends. They have never met before. They don't even know each other's names and yet they're running around, laughing, playing make believe and just enjoying each other's company.
Why can't we as adults do that? Why is it so hard for us to just jump in, with that child-like innocence and make new friends, in the moment. I think, for me, I feel like it has to be some sort of long-term relationship; that it's gonna take a lot of work to maintain and so on and so on. But really, it doesn't. I could have all kinds of friends; just people I meet in passing or at the grocery store or whatever. People whom I may never see again, but friends through a casual conversation or even just a smile, a connection that can last a lifetime. Wow, I learned a little somethin' today, from my sweet little somethin'. It's funny what we can learn through the eyes of a child.