The MC is reborn as an aristocrat child or a prince, and when he is five and a half years old, he disguises himself so can go to a guild in to be on an adventure. When he becomes an adventurer, he goes to a forest to search for some medicine plant but meets with an orphan boy, who is attacked by a wolf. He saves him and becomes friends with him, later coming to his home and healing his sister.
This is The Child Loved By God, aka Kami ni Aisareta Ko
An old person who had piled up good deeds in Japan reaches the end of his life, and is reincarnated into another world as Lean Olgott, the grandson of a certain king. One day, the boy, who was raised showered with love by his family, noticed that he had been bestowed the title "The Child Loved by God." ...
He reincarnates as a prince at birth. At the age of 6 he goes out and registers as an adventurer - just to gather herbs, but ends up encountering a wolf attacking another child adventurer. He saves him, and ends up going to meet his sister, healing her immediately with a prayer.
Found by searching mangaupdates.com for the tags