1.It's high time that our child ______ to wash her own cloth

1. 固定句型：
It's （high) time that + 主 +过去式（表示对现在事实相反的假设）...(high是强调的）
It's time that we left.该是我们离开的时候了.
也可以说：
It's time for us to leave.意思一样.
2. suggest“建议”的意思时就用.
建议……应该做……（还没做）（should可以省略）
suggest“暗示,表明”时,就不用这个结构了.因为从句中的动作往往已经发生了.
如：
I suggest that he (should) leave soon.我建议他（应该）离开.
His expression suggested that he had known about it. 他的表情表明他已经知道这件事了.

第一题
It is (high) time that后面的从句谓语动词要用过去式或用should加动词原形，但should不可省略。
It is time that the children went to bed.
It is high time that the children should go to bed.
it's high time that ...

1.It is high time that + 一般过去时，表示一种虚拟语气，这里你看看那个是一般过去时？B吧？那就是了。
2.用于提议时候，这个句型就可以用。比如说，Our teacher suggest that we finish homework today.（老师建议我们，今天之内就把作业做完）
如果你有不明白的，欢迎追问...