This could be one of several things.
It could be that it's just his normal coloration. Many boys have a naturally pinkish/reddish foreskin tip, especially fair complected boys.
It could be that he's been paying a little bit too much "attention" to it if you know what I mean and he has irritated it.
It could also be that he has a low grade infection that his immune system is fighting. Eventually if this is the case, something will happen. Either his immune system will gain control of it or something will happen to temporarily diminish his immune system and the infectious agent will flourish and the symptoms will become quite noticeable. If you suspect an infection, you can try to give his immune system a boost by applying plain unsweetened yogurt several times a day for a week or 10 days. The active cultures in yogurt are the same protective bacteria that protect the preputial space.
Unfortunately, over the internet we can not diagnose the problem and ultimately, you may have to seek competent medical care. Just make it very clear from the very begining that he is not to be retracted to any degree and stand close by ready to take physical action just in case. If you see any indication the doctor might be ready to retract, grab his/her hand and stop it right there. The other option is to tell the doctor not to touch his penis and you move it around as necessary for the doctor to examine it and take samples for a culture.