Chittai Ore no Makikomare Isekai Seikatsu

A tired middle-aged man gets caught up in a "Saint Summoning" and is reincarnated in another world as "Infant Keita" along with a (bitchy) high school girl! Keita is uneasy about this world that the goddess supposedly created to pass the time, but with magical powers that surpass those of the saint she was given upon reincarnation, wisdom and generosity from his previous life, and above all, his adorable little form, he is cherished by the kind inhabitants of this other world ♡ He enjoys his time in this laid-back other world while being held in the arms of the third prince who acts as his guardian!

(Source: Futabasha, translated)