一
Don't let the children stay up too late on weekends,will you?
Don't let the children eat a lot of sweets,shall we?
这组句子后面的附近疑问词为什么会不同?语法书说不是只有let's的时候才用shall 还有这里为什么不能当做祈使句来处理呢（就是祈使句的否定形式啊,就该填will you了）?
二
She had her hair cut the day before yesterday,didn't she?
You had your watch repaired yesterday,hadn't you?
这2个句子,看不出来结构上有什么不同.为什么它们的附近疑问部分,会不同呢?