He said any parent found guilty would be prosecuted.
Shettima gave the warning on Wednesday while addressing parents whose children are beneficiaries of the free-basic education introduced by his administration.
He also presented parents with incentives, which included food items and wears, as part of efforts to encourage them to send their female children to school rather than selling them off to marriage.
Shettima said: “Allow them to finish secondary school; irrespective of all the assistance and hospitality we offer you, whoever marries out his 12-year-old daughter would be prosecuted.
“We as parents must help them acquire western and religious education.”