What the Law says...
Under Article 45 of the Education and Libraries (Northern Ireland) Order 1986 (“the 1986 Order”), it is the duty of parents who have a child of compulsory school age to ensure their child receives efficient, full time education suitable to their age, aptitude, ability and to any special educational needs they may have. Such education may be provided by regular attendance at school or otherwise, for example home education.
Paragraph 3 (1) of Schedule 13 to the 1986 Order states that it is the duty of a parent of a registered pupil of a school to secure their regular attendance at school. This applies to all children of compulsory school age who are on the roll of a school. As a parent you are legally responsible for making this happen.
Under Part III of Schedule 13 to the 1986 Order, if a child or young person who is registered at a school does not attend regularly, a parent can receive a fine not exceeding £1,000 in court (for each child). An Education Supervision Order (ESO) could also be made by a court under Article 55 of the Children (NI) Order 1995.
Further detail can be found at
https://www.education-ni.gov.uk/sites/default/files/publications/de/attendance-matters-a-parents-guide.pdf