Honestly it can go either way at that age, some babies are totally fine and some do get a bit of a rash from the sand or saltwater. I would say try a short trip at a cooler time like early morning, bring a mat so he's not directly on the sand the whole time, and wash him off well after, then just watch his skin for the next day or so to see how he reacts. If his skin is already sensitive or has eczema patches, maybe hold off a little and check with your PD first before the trip.