I should also mention that, in my opinion, 'childish' stories also have a place in literature. Light-hearted entertainment can be endearing, heart-warming, uplifting or even thought-provoking. I mean shounen manga/anime is probably as childish as you can get and yet people much older than the target audience enjoy it anyway. But again, those are just my thoughts. It goes without saying you should be you and do whatever feels right - not that you need to hear that from me ofc. I have no writing talent myself after all I'm more a math guy