Pre-kindergarten children have probably been familiar with numbers for some time. They may be able to tell the difference between a number and a letter. They may be able to identify the shapes of some numbers and recognize that they often appear on mailboxes and apartment doors. They may be able to count to 10.
What will most likely be new is an understanding that numbers mean something. They can help you understand and navigate the world. If you're lost, they can tell a police officer how to call your mom and get you home. If you're bored in math class, they can tell you how much longer it'll be till recess. Three of them in a particular order can even help you save a life.
Kindergarteners begin learning how to tell time, count all the way to 20 (or beyond), dial 911, remember addresses and phone numbers, and start to acquire a sense of addition and subtraction by adding and taking away physical objects from groups.
And finally, the lesson as big as the universe ...