Because the wireless settings didn't change...

it seems that both your wireless mouse + keyboard transmit datas by bluetooth, but bluetooth use the same wireless frequency as 850RE, so there will be serious wireless collision when you start to...

How many signal led lights are on?

May be you can try the newest firmware on the UK company website of TP-LINK.

You can refer to this FAQ to set up Parent control on your VR900. http://www.tp-link.com/en/faq-927.html You need to use the virtual mac displayed on the web page of VR900 to set up parent control.

http://www.tp-link.com/en/faq-698.html You can refer to this FAQ to set up your 850RE.