For me, I think "Rules for disciples" is not only for children, it also has significant meaning for adults as well.

《弟子规》was written by 李毓秀 in Qing dynasty,and is known as ‘Disciple gauge’ in English."弟子" usually means little children,especially who are beginning to study;however some scholars think that it means students because all the students of Confucius were called “弟子”in ancient writings."规"means rules.《弟子规》not only tells people some basic etiquette but Chinese traditional culture, literature, history, philosophy, astronomy, geography, human relations and moral principles, filial piety, etc.its main idea includes“仁Benevolence，义righteousness，诚honesty，敬respect，孝filial piety”.

《弟子规》 was formerly known as 《训蒙文》, written by 李毓秀. The official English book name is 'Standards for Being a Good Student and Child', so... you know what was it used for... Hope this can helps you out.