It strongly depends on the country you live in. Regulations will be quite different in Saudi Arabia and in Germany.
In Germany, many local regulations allow children up to 6 years to stay naked in swimming pools, while on beaches staying naked is perfectly OK for adults too. However, it wouldn't be allowed to run naked in park, but in case of children, as long as nobody gets offended it should be OK.
Generally, people shouldn't feel offended by naked children, because children are no danger for them. That are adults that are potential danger for children, not the other way round. But it's highly culture-specific.
If people start complaining, I don't think your son would still feel comfortable with being naked. But as long as other people are OK, there's no need to restrict him, in my opinion.