is there any way to block access to free wifi to kids' home computers?

Hi, 

I just realized this is is going to be a completely non-router related question. I will ask it here anyway in the hope to get some advise. 

In our area, we have free wifi access. I would like to have kids not access public wifi from home and instead only use internet using traffic routed by our home router for better monitoring site visits. 

Do you know way to block free wifi access on Windows and MacOS computers? I have root/admin access of those laptops, kids don't. 

Thanks!