In My Bus by Byron Barton, Joe the driver keeps track of which passengers--a mix of cats and dogs--board and depart from his bus. Children can follow along and see exactly how many cats and dogs are traveling at any given time.
Barton keeps the dogs on one side of the bus and the cats on the other, for easy tallying. He never explicitly states "1 dog + 4 dogs = 5 dogs," but mentally children take note of how many are on the bus. It's a brilliant way to make young readers aware that they sort out and sum up the things in their world all the time.
There are four people in a child's family, let's say. Two have arrived at the dinner table; we're waiting for two more. One clears the dishes after the meal; three are still seated at the table. There's no fancy addition or subtraction; it's a simple way to be mindful of what's going on around them.
Byron gives children other things to look at, too--a boat, a plane, a train. And at the end of My Bus, the first dog passenger that boarded the bus leaves with Joe the driver: "I drive one dog home. My dog! Bow wow." (And for cat lovers, one cat ends the book: "Meow.") Satisfying in every way.