What are some tips for monitoring kids' cell phone activities?

If u want to know abt browsing history and stuffs u can visit Google - My Activity
U can access if u know which gmail account is used to signing in their mobile and it is possible only in android phones .
U can download from Google Playstore ( Android Device Manager) to know the device location and u can access only with the gmail account which they ised to sign in to their mobile and it can be done only in android phones.

Thanks for the thread here! I needed such an info too. I can also recommend you to use mobile tracker software for Android from https://www.hoverwatch.com It will help you monitor your kid's activity over the Internet, which is really important these days...