Rules didn't mean as much to later children in the family这里a

as much 相对同样多的
to 这里应该只作介词
later children 应该和later childhood一样,是少年期,学龄儿童期的孩子的意思
意译的话：条条框框的对于家中的小孩子来说没什么意义（没那么大约束力）.