I have a 6 year old grandson that is crying, doubled over, saying his left side abdominal area is hurting. I had him lay flat on the floor and felt around on his abdomen. There is no bumps or hard knots. I then had him stand up and raise his arms straight up, like he is stretching, and he hit the floor into a ball.
I now have him laying flat on the couch with a heating pad on it, to see if it helps any at all. Not sure if it is a muscle or what else it could be.