Tensei Kizoku no Isekai Boukenroku: Jichou wo Shiranai Kamigami no Shito

In both main character is reincarnated as an OP small child by gods who take an active interest in his life. They also both become talented and high ranking adventurers in very little time. 

another story that start out similar way... although the reason for dying was a different in both show the mc is unaware at first that he is very op due to the deities blessinges, in one the the mc is aware but in the other is unaware of it power but end up both related to the royalty. 

In this anime, the main character is extremely strong, while he also tries to hide his real strength so that people do not know, the main character is also friendly, trains a lot and tries to help whenever possible (the main character, as for me, these qualities stand out perfectly, while he is not very reasonable because he solves everything quickly without thinking about the consequences and bonuses, the main character's boss is the king, just like here, and the main character is also studying at the academy). In my opinion, it is perfect, I have described these qualities and factors that stand out strongly and are very similar to this anime. read more 

Both MCs are reincarnated as a child in the royal family, over powered 

Both MCs are reincarnated as a child in the royal family, use knowledge from other world to help themselves. Both over powered.  

Male reincarnates in fantasy setting as OP MC blessed by gods. Creates harem with OP abilities, a kind heart and plot armor. Plot focusses on world building w/o a concrete villain 

Similar feeling Isekai, also has OP child dragged into running a country whilst trying to fufill a alternate goal.  

Both feature an op isekai MC on steroids and a harem somewhat.  

Same plot where the overpowered MC will marry at least one princess and get a land to build his dream and save other lands and kingdoms  

MC dies and reincarnates into a fantasy world (Isekai). Both Isekai stories start from their childhood. Both MC's get girl tutors as kids. But they are way stronger than their tutors. Both MC's are overpowered. Both series have comedy elements. 

Both MC's reincarnate as a child into a royal family and possess a lot of magical power.