No. Naturism is about nudity, hence underwear, bathing costumes and other bits of clothing are redundant. But, there are times when clothes make sense such as when it is cold.
At the naturist resort we frequent almost everyone puts on something substantial when it rains, at least a T-Shirt to keep the chest warm. As it gets colder bottoms are worn. But, since the idea is to get naked the most desirable situation would be to just go somewhere that is warm so you don't have to get dressed again. A cosy fireplace always does the trick.
An exception to the nudity rules at these resorts is that children under 18 can wear what they want. This may be different at different resorts & beaches but, in general if you are under 18 the decision as to whether you undress lie with your parents.
Still, I've never seen anyone running around in their underwear. What would be the point?