My 4 years old son start reading for a few months, and his teacher said that his reading level is in 2nd grade, I would like to ask how do I know which book is in which reading level? I am thinking to choose some "2nd grade" books for him to read but his understanding of the world is still a 4 years old, so can anyone recommend some books that is suitable for a 4 years old with 2nd grade reading level to read by himself? Thanks a lot.

He loves books about hide and seek, play with friends, sth like that, but not those complicate content in fancy nancy.

and I also want to introduce him sth about magic, hero, peter pan, fairy, is there any short picture story books of these topics?
As i find most are very long stories that my son doesn't enjoy. Thanks.