Kids don't have any problems, really. No preconceived notions of the world that surrounds them, they don't judge others based on superficial values, and they don't care about biological differences. All these small things change over time, thus making them into those grown-ups they so want to become. What they forget, or rather, they don't even think about, is how that path is making them change.
When you are just a small kid going to kindergarten, you play around with anyone, as long as it is fun. Later in life that's just not how it is. Once you're in elementary school, you'll choose a small group of people, maybe only one, to be around at all times. That's when you start making friends. These friends will be around for some time, but this friendship will break at some point, for one reason, or another.
