Yes, a rash guard can keep you warm, but not as affectively as wetsuits. Rash guards are meant for light activities in the water, where you won’t be going to deep depths. For kids, scuba diving isn’t really a safe activity, so a rash guard will offer the perfect amount of warmth for paddle boarding, surfing, a day at the beach, or the pool. A long sleeve rash guard would also add more warmth than a short sleeve design.