I'm trying to remember how old he is; isn't he around 3? By that age, my kiddo had discovered the word "why" and would say it constantly. He talked and wanted attention pretty much every moment he was awake. I suppose he'd have been as sloppy with an adult cup as Atlas is, which is why you don't give one to them. If you're trying to train them to drink out of one, do it during meals when you're sitting with them and can clean them up.
It bugs me that Atlas wanders around barefoot and in what looks like pajamas all day. Do they not have any cute real clothes for him? No jeans, no cute sweatshirts or t-shirts, no real trainers? Robyn seems to buy a lot of girly cute outfits for Luna but I swear sometimes she makes Atlas wear her old pajamas.