the children their teacher often -------- for half an hour i

你所给的句子不完整,可以表达为下面的形式：
The children their teacher often【runs】 for half an hour in the morning(run) 【are also fond of sports】【复合句】
their teacher 是定语从句的主语,单数,谓语动词用单数.
or
The children 【and】their teacher often 【run】 for half an hour in the morning(run）【简单句】
The children 【and】their teacher 由and连接并列主语,复数,谓语动词用复数.
祝你开心如意!