Partial defense : I don't think its bad thing for them being reincarnators as kid. In other manhwa, most mc who are reincartors know what's going to happen because they have read the book or been through the scenario. Here the main characters doesn't know anything; they don't know the rules of the world, how it works, how to socialize and other stuff. They still learning and they are surviving. Maybe they'll used their past knowledge in the future but right now, i think it's fine if they're acting like children. (Also they died at the age of 18. They're not the type of adults that knows everything yet...... except the trusting stranger part. Idk why they trust him. Maybe the next chapter will tell? )