'You can't grow down, you can only grow up'.

Coco and Charlie are playing at Bing's house when Coco spots the measuring lines on the wall that show how Bing has grown. Flop measures Bing and he's bigger than the last time. When Bing can't reach his paper aeroplane, Coco offers to measure him again to check if he's really grown but they don't quite get the measuring ritual right and the new mark is much lower than before. Bing gets scared that he's growing down and that if he keeps going he'll be as small as Charlie.