How does it not break your heart?

We go to the playground and Mary's the youngest by a few years. This doesn't bother her in the least. There are 4 big girls- age 6-8. They play a secret game of cat and mouse. They go to one area. Mary follows. They run away and congregate somewhere else. She follows, again they scamper. She doesn't seem to mind. It's a game. To me, it hurts. I just want to grab her and shield her from all the rejection in life, but I know it's a part of growing up. I can't protect her forever. The girls crawl in a tunnel. Mary politely asks, "Please, may I come in there with you?" They scoot over and make room. She's so happy. She looks at me and smiles the 100 watt grin of hers. I'm thrilled that she used good manners. She wedges herself in, they crawl out. She smiles and follows. The game is back.