The children promised to be careful and that they would retu

问题在于前后结构不一致
promise to do sth.或者 promise that 从句
而在这个句子中,它却把两个不同的结构用于同一句子中
正确句子,the children promised to be careful and return home earlier.
或者,the children promised that they would be careful and return home earlier.