أرجوا الأجابة على هذا السؤال نظرا لأختلاف الأجابة

[aymanaziz1]

The only answer is don't have to

Because don't have to means it isn't necessary

In this case we can't use mustn't
Because mustn't means it's forbidden

In Egypt children can go to school under the age of six but some parents don't prefer to let their children go. So it isn't nessary