Several cultures in which child marriage occurs customarily do not consummate the marriage until the girl hits puberty (which has steadily declined in recent years; there is also evidence that menarche begins later the more rural a girl's environment so a rural girl might be 14 or 15 before she has her first period).

I don't know what culture you come from, but twelve isn't all that young for Western cultures. The age of consent in Europe averages 14-15 with Spain at thirteen.