Love the buttons as balloons! Nice way to use a batch of buttons that are different. Stamp the birthday sentiment in different colors down the side and add a dimensional cut out for this handmade birthday card.
I see this done with the Artbooking Cricut cartridge. Choose your recipients favourite colours, pop up their birthday number (if it's a significant one), add some bling (if it's for a girl), buttons, cake or a car for a guy & you're done.