My son stood on something a few days ago. he is 4 years. it looks like a nail hole or something points. it was red around the wound but now its the puncture hole with a white ring around and then a reddy purple around the white ring.

Get him evaluated: A puncture wound of this type can provide easy access for germs to the deep tissues/ligaments of the foot where a deep infection can arise and eventually require surgical drainage and hospital care. I would contact his doc and discuss the issue. He will likely need to see him to decide if this can be managed at home or needs immediate aggressive care.