Hey! I also joined Wanikani with previous experience with Minna No Nihongo.
As others mentioned, children’s books can have more advanced grammar so I agree starting with graded readers might be a bit better. Check out this free link to be able to read high quality graded readers with audio until the end of the month.
I ended up buying a level 0 reader before I found this link and after reading the books there I really wish I had just gone straight to level 2 readers. Hope this helps you find your comprehension level as well. 