You don't have to tell him twice.It seems he disappears right when you reach the campsite, so telling him to explore more seems as redundant as telling him to eat more candy. However, it might be nice to warn other parents of his exploratory habits, and Meridian Line couldn't have said it better than the Boys' Explore More T-Shirt.
Summer-worthy shirt for pursuits of discovery
Tri-blend fabric is breathable, quick to dry, and smooth as a river stone
Item #MRD0021

Material50% polyester, 25% cotton, 25% rayon
Recommended Usecasual