Soda causing nosebleed?

Soda does not thin your blood. As a general rule thin blood will not cause a nose bleed unless it is so thin that it is causing other problems. The culprit is more likely caffeine in the soda. Caffeine raises blood pressure. Elevated blood pressure can cause nose bleeds. Also this time of year the air tends to be dry and that can cause nose bleeds as well. When I was younger I used to get nose bleeds all the time. My mother, who is a nurse, looked in my nose and found a large clot (about the size of a baby mouse). When she pulled out the clot I stopped having nose bleeds. If it does continue you should take your son to the doctor to rule out some other serious things that it could be. I won't tell you what they are because I don't want to scare you.