just to elaborate on Shelke's link (I.e. it's alright if you know where to look once you've logged in).
Log in to your account > then click on the "Plan and device" tab from the row near the top of the page.
This takes you to a page "My tariffs and devices" & "Manage my services" with the "switch" for Parental control is there.
Once you've changed the setting. Allow time for your account to update then reboot your phone by turning it off & on again.
If you want to say thanks > click 'Kudos'.Answered your question? > click 'Mark as Helpful Answer' also.