Under black codes, African Americans children found to be vagrant were often

Forced into convict labor until they were adults.

Explanation:

The Black Codes were a series of laws that were passed on the Southern States to limit African American's rights.

The Vagrancy Act of 1866 determined that anyone that appeared to be unemployed or homeless would be forced into employment for up to three months. Often kids that were walking to school would be considered vagrants and forced into forced labor.

the answer is forced into convict labor until they were adults