I presume he is out of nappies, which reduces one cause of soreness and infection.
Some anaesthetists/surgeons inject a long-term local anaesthetic for pain relief while the patient is still asleep. Waking up with a 'dead'-feeling dick can upset some kids. This needs to be discussed with the medical staff beforehand, to see if they intend to do this and with your son if they do, so he knows it will eventually feel normal, if sore initially.
Some surgeons opt for a preputial stretch, where the opening of the foreskin is stretched under anaesthetic, rather than a circumcision.