Final answer:
The question about the three boys building sand castles does not have specific individuals identified but is part of an Arts context, where students can learn about activities related to sand through various artistic depictions.
Step-by-step explanation:
The three boys building sand castles are not detailed with specific names or identities within the provided references. However, to understand this concept in the context of Arts, we can refer to the last reference where it is mentioned: "Playing in a sandbox is fun for young children."
This is perhaps the closest in describing an activity where one might find children, such as the three boys, engaged in building sand castles. Most of the provided references involve depictions or activities at or near a beach, however, there's also reference to historic art pertaining to ancient Egypt's sarcophagus and the famous sculpture of Laocoon and his sons.
These are examples of art that illustrate activities and figures related to beaches or sands, allowing students to learn about the world and history through artistic depictions.