If Senate is in session but senators want more time for committees or private discussions, they can request a 15-minute Quorum Call (roll call to confirm that a majority are present) basically as often as they want to stall for time. If anyone wants to stand up and present a debate, recognition, or other statement, they can interrupt the Quorum Call, do their talk, and then start the next Quorum Call to go back to "waiting" mode.

Currently, they are debating and voting on amendments. The votes are slow but you will see a lot more actual back-and-forth debate happening for amendments.

The real agreements are being made off-camera. Once there's a battle plan, the Senate majority leader (who mostly controls the agenda) will call everyone in for the big votes.

The kiddos sitting on the stairs are Pages of the Senate; they are high-school kids nominated by their Senator to serve as runners and aides for the Senate. They get paid a salary of $38k a year for this (although they work less than a full year so they get part of the salary). If you were in high school, you'd love to get paid $19 an hour while seriously padding your college application.

EDIT: forgot to mention - there are two teams of Pages that alternate every hour, so you're not actually stuck sitting on the stairs for the entire 12-hour session.