This is Returning With Absolutely Nothing. It is licensed by Tapas.
In Aeria, a place where people from various worlds are summoned, the weak are destined to die. Lee Sungmin, a talentless mercenary, was no exception. Fortunately for him, a mysterious item he finds before his untimely death sends him back to the past. Now a 13-year-old with a second chance at life, Sungmin begins his desperate journey to become Aeria's strongest with no money or talent. The question is... will effort alone be enough to make a hero of a boy with absolutely nothing?
The story opens with the main character being summoned to another world; seemingly for the first time, but when someone tries to poison him he turns the tables on the assailant as he already knows the trick. It's revealed that he went back in time 13 years to when he was first summoned. He is explicitly referred to as a C-rank, and a "classless"
He's not quite talentless; besides knowing future events, it's stated that the classless have higher growth. They just usually don't live long enough to do anything with it, as they're initially very weak.
In the second chapter he runs into a small child as he's first summoned;
and realizes that this person is a master martial artist that was summoned at about the same time as him in his first life.
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