omg i remember reading this too but i can't remember the title
Damn if anyone remember let me know
Hold up is there a skeleton in the story? if so I know it
Sodatetchimaou is what your thinking of.
YES YES THIS IS THE ONE!
its actually spelled Sodatechimaou. its spelled differently on other sites too.
like Sodatechi Maou! on mangakalot.
This reminds me of another series with the same genre. I forgot the title but it's also about a child wondering into the demon realm and the 3 demon King brothers raised him! (≧∀≦)