When you get a report showing that your kids are well above the average articulated is should not be surprising. The question what do you do with it?
There is a web site to access a database of books according to Lexile level, genre, and maybe some other categories.
My dd received her first Lexile score in 3rd grade (8yo). I don't remember the number right now, but it was very high. So I put in her score and the genre "humor" to see what would turn up in the database. I think there was only one book returned by the query, and it was a very long academic treatise on humor. LOL! My conclusion was that for our case, the Lexile score was not so useful -- dh and I got to be pretty good about finding (many, many!) books that matched her interests and depth needs.
We are strong proponents of the notion that in selecting books, child engagement is way more important than stretching their reading level. For our kids, the latter followed the former pretty much effortlessly. And yes, among other things, we read tons of humor below both our reading and maturity levels.
