This app was mentioned in 9 comments, with an average of 1.22 upvotes
Here are the ones I found searching through Google Play. https://play.google.com/store/apps/details?id=com.nationaledtech.spinbrowser&hl=en This one is aimed at kids but it seems to be a promising safe browser. https://play.google.com/store/apps/details?id=com.imlock.android&hl=en There is also this one but I think this one requires you to pay for it. The version of android that is required for those apps above to run is android 4 or above.
You can use a safe browser such as "SPIN Safe Browser" (https://play.google.com/store/apps/details?id=com.nationaledtech.spinbrowser&hl=en). I like it because it is very strict. This does not prevent you from accessing porn through another browser (Chrome, Firefox, etc..). So you need to block all the other browsers with apps like "App Detox" (https://play.google.com/store/apps/details?id=de.dfki.appdetox&hl=en).
You can use OpenDNS Family Shield too (https://www.opendns.com/home-internet-security/). It is very powerful and it is free. You need to change your DNS to
208.67.222.123
208.67.220.123
This allows you to protect the wifi network. To protect the mobile network too, you need to use an app to change DNS on your android phone. I use an app which does not require rooting the phone (https://play.google.com/store/search?q=dns%20no%20root&c=apps&hl=en_US).
Child-friendly launchers:
Misc:
install some porn-block browser: *SPIN Safe Browser *(Google Play, apk)
ShieldMyTeen Parental Control(Google Play, apk) this app will block grey websites, contents.
Cloudacl Safe Web Browser is cloud based content filtering safe web browser which monitoring millions websites and billion of webpages (Google Play: https://play.google.com/store/apps/details?id=com.cloudacl, apk: http://choilieng.com/apk-on-pc/com.cloudacl.apk)
install some porn-block browser:
*SPIN Safe Browser *(Google Play, apk)
ShieldMyTeen Parental Control(Google Play, apk) this app will block grey websites, contents.
Cloudacl Safe Web Browser is cloud based content filtering safe web browser which monitoring millions websites and billion of webpages (Google Play, apk)
I use SPIN browser https://play.google.com/store/apps/details?id=com.nationaledtech.spinbrowser&hl=en
Just make sure to disable your other browsers in system settings.