In an earlier scene, Mitchell bumps his daughters head on a doorframe, but then begins to worry that he may not be ready to have a child. Mitch sees how much Lily likes Cam and how good of a caretaker he is and begins to worry that he is a worse parent, but Cam reassures him that they are both great parents because they complement each other. Their decision to specialize in particular tasks allows them to complete more work together and both recognize they wouldn’t accomplish nearly as much if each had to go it alone.
See more: comparative advantage, complements, division of labor, household production, household labor supply, interdependent utility functions, labor supply, specialization
When Mitchell realizes how cheap items at CostCo are, he suggests getting enough for the next two years. When he realizes how many diapers that is, he thinks about getting a shed to store them all. When people face steep discounts on prices, they respond by buying more (law of demand), but how much more they decide to buy is based on the elasticity of demand. In this case, Mitchel appears to be a very price sensitive buyer even though the items are really necessities.
See more: complements, demand, elasticity, income effect, prices, quantity demanded