The Doctor looks a bit surprised at her knowledgeable advising, but she's definitely got a point. He sits down crosslegged, and starts to scoop sand into a big pile, using only his hands despite the ready availability of shovels in a dream. Buckets have a place, but finer tools are only for detailing, in his opinion. "Hm, yes. Very practical." He'd rather always thought the moat was the most important part. Time tots are not especially invested in sand building, but why would they be? It's a valuable lesson in transience and impermanence, which they probably didn't especially need or wouldn't be able to properly appreciate. Maybe if Rassilon had built more sandcastles, though. Just a few. "Earth sand isn't usually this colour; white or yellow is more usual. On the right Earth beach, you could build a castle more like your dream city place." Not at all a perfect match, it would never be so horrifyingly, aggressively yellow as her room's colour scheme, but closer than this.