The child's mother, Kancy Barerra, 22, told police that Hidalgo was holding a black handgun for his cousin, the Morning News reported, citing an arrest warrant.
According to the affidavit, Hidalgo told police he was in the bathroom with Barrera when he heard a loud noise, the newspaper reported. He said he found the child standing in a nearby room crying, and that the boy had shot himself, according to the affidavit.
Hidalgo remains in the Dallas County Jail, the Morning News reported. Bail has not been set.