views expose filter by taxonomy
You can do this with the special type of filter Has taxonomy terms (with depth). 


Add a new Filter Has taxonomy terms (with depth)
Select your Vocabulary in the new filter settings,
Selection type: Dropdown
Show hierarchy in dropdown
Depth 2 (this will include 2 levels of children of a chosen term)
Expose this filter to visitors, to allow them to change it and Apply 


You will get a drop-down that shows your terms with hierarchy. 

If you don't want a dropdown you can use a module like Better exposed filters to use radio buttons instead.