In your position, I’d start with local control - you can do this with your existing devices. They’ll still be on wifi, which isn’t ideal, but you should get much better response times when your devices are just pinging a controller on your local network instead of a cloud server.
Once you’ve got local control established, then I’d start looking at gradually upgrading/replacing devices.
Hmm. There are lots of smart plugs available, and lots of options in terms of hubs etc depending on how much fine grain control you want and whether you want to be able to add more different types of devices in the future. But my question would be, what’s to stop the kids just unplugging the smart plug and plugging the tv straight back into the wall? It’s what I would have done!