I had the same question before our first cruise.
They don't have access to any soda places in the clubs. They do have a water fountain in the club/lab for them if they are thirsty, as well as a restroom. For those times they are away from the clubs (like the sports deck), they seem to work bathroom and drink breaks together, and use the public areas.
Even if they are up on the top deck (such as the scoop visits), they won't let the kids get sodas with a mug (or sticker, or paying for them with KTTW cards). I can understand that some kids wouldn't understand why Johnny has a coke and I can't, so they just avoid the whole thing.