In the evenings I frequently have multiple devices going at once:
My TV streaming Netflix while I flip through stuff on my phone
My wife streaming some other show on her ipad while flipping through stuff on her phone
My kid playing some online game while watching something on his ipad
And my wifi seizes up all the time (for all devices) and I lose connections and all sorts of other shit.
Here’s a easy test. For the next hour only you are connected to the WiFi (I assume that you have a passcode and that your neighbors aren’t using it too). Do you notice any problems? If not, add your wife and run that for an hour. Still okay? Add your kid. In other words gradually increase the number of devices until you start noticing the problem. Perhaps you need a more robust router. New ones that are probably better than the one you have can be had fairly cheaply these days.
Do you (or even the neighbours) use Powerline networking - those devices that plug into the mains and route network traffic through your electrical wiring? They’re notoriously dirty in terms of interference, and I traced weird WiFi disconnections to a Powerline unit I had set up.
In your scenario, everything you are doing is going through the connection (DSL? Cable?) to the internet. Unless you have antique devices or Google Fiber internet, there is an order of magnitude more bandwidth in WiFi than internet service.
However, most “home routers” are crap. I found it better to buy an Apple Airport (about 3 inches square, 7 inches tall) for $200 after going through about a router every year at $50 each - they would intermittently fail, lose connections, need reboots, etc. The Apple has been rock solid for 3 or 4 years.
Plus, as others point out - possible interference. I used to use InSSIDer to monitor wifi neighbourhoods, but I see it’s not free any more. There are alternatives:
This is why I prefer high speed internet connection with a ethernet cord into a usb port because the connection is more stable. Wifi connection is too inconsistent
I don’t know if it is relevant but my daughter had problems when she stood her router next to her TV. A TV gives off all kinds of radio frequency noise and that was disrupting the signal.