I have AT&T router. Under there setting do not have any parent control. IS other way I can block some websites via wifi. So Kids do not have access.

The best form of Parental Control is monitoring their online activities in a public place, like lounge or dining room.

Software blocks and monitors are easily circumvented.

You will need to put blocks on their individual equipment. But best as noted, do not allow them use of computers outside of the main living area, Be in and around the rooms they are at using computers, check history files of where they go and so on.

Any precautions you can set in place they can disable have them use the computers in a area visible to you. OpenDNS.org offers filtering based on DNS co you configure your filtering and set the router to get DNS from Open DNS and that will work and it can be circumvented.