My policy says they can come if they can continue with the normal activities of the day.
In this case I would keep him if I could tolerate it and manage the rest of my crew. I would not keep him if he was too disruptive and he was unsettled by it.
This is a bit of a wishy washy area because there is no fever. Any chance the parent gave a dose of advil and dropped him off with you?
If its out of the norm for the child and I was concerned about his comfort level then I would call the parent. The crying concerns me more then anything else.