My friend, Loonie / Nina LaCour ; illustrated by Ashling Lindsay.

Enhanced descriptions from Syndetics:

A gentle story of connection and loss finds a promise in memories after a young child loses her constant companion.

With a good friend like Loonie the yellow balloon, anything is possible. From neighborhood walks to reading aloud in bed to dance parties in your room, Loonie makes each activity a little brighter, a little fuller of sunshine. But as one child discovers with sadness, when it's time for Loonie to float away home, the sunshine goes, too. It's not as fun to have a dance party alone. And while tending to the garden helps a little bit, the world outside the window is silent and gray. Until, one day, as flowers start to push up from the soil, big and full of hope, the memory of Loonie begins to emerge in unexpected places. With tender empathy, and charming and whimsical art by Ashling Lindsay, Printz Award winner Nina LaCour illuminates the childhood companions that bring a little magic to the world.