Numbers 14:29-31 states that God allowed those aged 19 years and under to enter the Promised Land, but those 20 and over would die off in the wilderness because of the rebellion.
Deuteronomy 1:39 Moreover your little ones, which ye said should be a prey, and your children, which in that day had no knowledge between good and evil, they shall go in thither, and unto them will I give it, and they shall possess it.
Moreover your little ones, which ye said should be a prey, and your children, which in that day had no knowledge between good and evil, they shall go in thither, and unto them will I give it, and they shall possess it.
This is past tense, saying that they HAD no knowledge of good and evil. Remember, the age group of 0-19 years includes toddlers and young children (under 12). But to say that all those under 20 are innocent and incapable of understanding between good/evil is completely false, because it contradicts other Biblical passages.
Joseph was 17 years old when God gave him a dream (Genesis 37). In this dream, God told him about his future of ruling his brothers.
Luke 2:41-49 is where the Lord Jesus Christ impresses the Temple elders with His wisdom, and He tells Mary and Joseph that "I must be about my Father's business." Clearly, a 12-year-old is seen as accountable for his sins in the eyes of God.
