This stage is Pretty Plaza Panic (3-4) . This complete walkthrough will provide you with a 100% video playthrough and a screenshot of where you can find all the green stars. To get everything in this stage, you will have to use Princess Peach as your character.
Game Play Walkthrough Video
Green Star 1
At the beginning of the stage, walk towards you or the screen to pick up the first green star.
Green Star 2
When you get to a fountain with some coins, there is a green rabbit carrying the next star. Tackle him and claim it for yourself.
Green Star 3
Jump onto the smiley face cloud when you see it. Complete the obstacle course and grab the last star at the end.
When you get to the second group of spinning platforms, flip the switch with the crown symbol to reveal the stamp.