youtube video PG control

Information on how to enable Youtube's Safety Mode for parental controls may be found here:
https://support.google.com/youtube/answer/174084

how about Android phone apps, iPhone apps and windows phone apps? any control there?

what can we do after enable Safety Mode ?

what safety mode does ? I want to control my kids seems all video there and preferably only video I subscribe for an email account.

I use the free K9 Web Protection:
http://www1.k9webprotection.com/

but that one is not for android phone, right?

kids watch via youtube apps, so this SW do not apply ?

it seems that there are no menu on how to use it ?

For iOS:
http://www1.k9webprotection.com/support/set-idevice-restrictions

Seems is not very good documented for Android. I use it for Windows desktop.
In Google Play are many other free apps for parenting control for Android:
https://play.google.com/store/search?q=parental+control+apps&c=apps&price=1&rating=1

that apps keep having no response once launch

Have you tried to go to the K9 Administration page (http://127.0.0.1:2372), and click [Setup] and sign in with your current password?
I tried  it only with Windows and iPad and never tried with Android, but here seems an issue:
http://www1.k9webprotection.com/support/kb/K9170.html

"Have you tried to go to the K9 Administration page (http://127.0.0.1:2372), and click [Setup] and sign in with your current password?"

yes !

Then there is not well implemented for Android and remains to try other free  parenting control apps for Android:
https://play.google.com/store/search?q=parental+control+apps&c=apps&price=1&rating=1

The last thing than can be done is technical support:
http://www1.k9webprotection.com/support/contact

during that K9 apps launch, the whole phone seems freezed !