I want to a void my kids watch a specific movie ?

I don't think you can block a specific movie in the iTunes Store, the only thing you could do would be to use Apple Family Sharing if you have multiple devices, which has a ability to ask you for specific purchases used with their icloud accounts, and you can deny them or to put Parental Controls on the device:

• Use Restrictions on your iPhone, iPad, and iPod touch - Apple Support
• iCloud - Family Sharing