Bolesław was born in 966 or 967, the first child of Mieszko I of Poland and his wife, the Bohemian princess Dobrawa. His "Epitaph", which was written in the middle of the , emphasized that Bolesław had been born to a "faithless" father and a "true-believing" mother, suggesting that he was born before his father's baptism. Bolesław was baptized shortly after his birth. He was named after his maternal grandfather, Boleslaus I, Duke of Bohemia. Not much is known about Bolesław's childhood. His "Epitaph" recorded that he underwent the traditional hair-cutting ceremony at the age of seven and a lock of his hair was sent to Rome. The latter act suggests that Mieszko wanted to place his son under the protection of the Holy See. Historian Tadeusz Manteuffel says that Bolesław needed that protection because his father had sent him to the court of Otto I, Holy Roman Emperor in token of his allegiance to the emperor. However, historian Marek Kazimierz Barański notes that the claim that Bolesław was sent as a hostage to the imperial court is disputed.