@Kevin_Z 

Thanks Kevin. I understand that the range extender does not include parental controls but I want to know if it is possible to set up the router’s parental controls to stop my kids accessing the WiFi even if they are connected to the range extender. The links you supplied only applies to websites and not restricting all WiFi access such as TVs linked to the wifi

I bought the tp-link router on the basis that it had parental controls. It seems bizarre that to-link with all their technical capabilities would not have a work around for this.  

I have used the same range extenders with my ISP supplied router and been able to set parental controls from the router that work across the whole network. It seems that the set up I have now acts as two routers, one of which has parental controls whilst the other does not. Have I set up the network incorrectly or is it possible have a network of router and range extenders that limits access for specific devices at certain times?

If not the whole lot can go back to the shop and I will look at a different system.