These are The Avengers Level 1 Reader (World of Reading, Level 1)

The Marvel Heroes of Reading line of early readers is designed to offer reluctant readers, specifically boys, books that they will want to read by featuring characters they love. The series is broken into three levels that invoke the rigorous training courses their favorite Marvel heroes must engage in to perfect their super powers. In reading this series, boys will prefect their own power to read.
Meet the Mighty Avengers introduces readers ages 4-6 to the world of Marvel's popular Super HeroTeam that includes Iron Man, Captain America, Thor and the Hulk!