Contextual filter for taxonomy terms
You can use "Taxonomy term: Parent term" as contextual filter in your view.

Most likely you will need to provide a default value for the filter, such as "Taxonomy term ID from URL".

Provide a default value for your filter according to your preferred usage. The options for setting the default value of the filter should be self-explanatory. 

Since you didn't specify where this view is supposed to be displayed, I can't give any other insight.