This series is a little weird. While it's a returner variety of isekai, beyond the first couple of chapters, the MC is shown up by a bunch of children in terms of skill despite the fact that he's a grown adult in terms of experience and has awareness of future events and techniques.
Like why bother making the MC a returner in the story if he's going to be second rung to a bunch of kids? It's just embarrassing. If you're going to go that route just make him a normal kid without any prior life experience.