Show page with child terms when clicking parent term
Follow these steps


Create a view
Add a relationship "Content: Tags", (Tags is vocabulary name I want to show content for)
Add a contextual filter "Content: Has taxonomy term ID (with depth)" (you can provide a depth of taxonomy term here to display content, if set to 0 it will show content tagged with that particular term id only, if 1 then that particular term id + its first child term content)
And provide proper value for this contextual filter.


Here is the screenshot of view I've created:


Hope this helps.