Unfortunately not, I just happen to have been raised by someone who believes in this concept, and with a diagnosis of DID I have to be rather vigilant in how I talk to and treat my inner children, so to me it's a very specific coping mechanism.

I've tried googling something useful, but from what I've found just now it's either through specific a spiritual lens or geared towards psychology and integration of a personality.

For the first lens I can't recommend anything, that is truly up to you if something from that side interests you, I wouldn't know which take from the spiritual side would resonate with you.

If you're interested in the scientific psychological explanation of how DID functions (and thus give rise to an actual, separate inner child), I would recommend Ctad Clinic on Youtube. They have a lot of very interesting explanations on how the human brain deconstructs a personality when it is formed under traumatic circumstances in order to protect itsself. I unfortunately have no reading options on that front at the moment. Should I find some specifically geared towards inner children and how to communicate with them I'll reply to your comment again if you like.

I recommend Flowers in the Dark:

https://www.amazon.com/Flowers-Dark-Reclaiming-Trauma-Mindfulness/dp/1946764566

Oh you might try googling 'mindfulness inner child', there's too much for me to go through to say "oh this one nails it", but I do think that's a better middle ground for an introduction to the concept of an inner child :)