Loonette and Molly spend the day discovering light and heavy things. After reading a story about a balloon, Loonette finds a balloon of her own, which she thinks can lift her off the ground. She's too heavy, of course, but the balloon does lift Molly off the couch and into the garden.

Molly's birthday is approaching. She and Loonette hold a birthday party with games and costumes. They also have fun with big things compared to little things, particularly with a story about a gigantic cupcake.

The show opens with a flashback: Loonette and Molly can't sleep. They venture around their house during the dark before Loonette reads her about a Sleep Train's magical adventure. The next day, Loonette discovers Major Bedhead asleep on the job.

When Molly catches a cold while skiing, Loonette decides to knit her some new mittens. But when the yarn becomes a tangled mess, Loonette abandons the task and retreats to Granny Garbanzo's garden. Granny tells a story of how she had to practice knitting as a child. This gives Loonette the confidence to keep on trying.

Loonette gives Molly a special heart balloon, but after a short amount of play, the balloon flies away. At Granny Garbanzo's garden, Loonette, Granny, and Major Bedhead have fun playing circus with a single rope. At the end of the circus routine, the heart balloon returns to Loonette, which brightens Molly's day.