If it is mosquito bites you could try the insect repellant bands. I saw two different kinds this week (sorry I didn't pay attention to brands). Both are plastic bracelets that are soaked with repellant. I think both contained citronella and other "natural" repellents. One said it repelled bugs for 6-8 hours. Another said the repellant would last for up to 3 years if stored properly. One could be worn around the wrist or ankle. I think both were I the $5 range. I've never tried them so don't know how effective they are.
You could also check with the school nurse about sending insect repellant to school. You would probably need to fill out a consent form and he would need to go to the nurse to have it applied.
I know some people think mosquito bites are nothing to worry about. But there are more and more diseases coming from mosquitoes. West Nile is the most common. My brother and nephew just got over chikungunya which is similar to dengue fever. It is mainly found in Europe, Africa, Asia, and the Atlantic and Pacific. But it has also been found in the Caribbean and now they are starting to see it here in the US--30 different states including Florida, California, Texas, DC, North Carolina, and even Minnesota. Travelers to the Caribbean are bringing it home with them.