In mathematics, a function is a relation that uniquely associates each element in a set (the domain) with exactly one element in another set (the codomain). In simpler terms, for every input, there is one and only one output.
Considering the provided table, it shows a function because each day of the week (input) corresponds to a specific and unique number of children in the car (output). No day of the week has the same number of children as another day, and every day listed in the table has a defined number of children associated with it. Thus, the relationship between the days of the week and the number of children in the car meets the definition of a function.