The same thing happened with my oldest when she was that age. I always made sure she didn't have to poop (I still ask her if she has to poop when she says her stomach hurts, much to her embarrassment!

) and that she wasn't sick otherwise. Her doctor said it's very common for kids that age--and mostly girls--to have random stomach aches. There isn't really any rhyme or reason either, oftentimes. For Madison, would have her lie down until she felt better. It would be 5 minutes max and then she'd hop up and play, good as new. They finally went away as she neared 5.