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There are features in some routers that allow you to set up multiple SSID's and a wifi schedule. If your router has these features, you can set up 2 wifi networks with different SSID's and different passwords, and schedule one of them to be on and off at certain hours.

Oh yes. The ability to provide a second or "guest" network is a feature of many home WiFi routers. If you ever go into a business and you see two WiFi networks:

 JPS-Private
 Joes Pizza Shack Free WiFi

That's exactly what that is. It simply has an internal firewall between the "guest" WiFi and the private network.

And many of these routers also have the feature to only enable the guest network at certain hours (e.g. Their business hours).

This is an easy feature to add to routers, and I see it in many. So just shop around (this stack is not a shopping help site) and you should find those features in a good number of routers.

I appreciate this is a tech questions site, and you’ve asked an appropriately on-topic question. However, I believe you’ve asked an XY question and this is actually a parenting problem, not a tech one.

Disabling or blocking your WiFi does not address the root cause of your problem which, reading between the lines, is that you’ve told your kids no internet after 10, but they disregard you. Confiscating devices, banning devices from bedrooms, and just making sure your kids respect you enough to follow your wishes/commands might all be better solutions. You might want to look for similar questions (or ask a new one) on Parenting SE.

If your current router does not support two wifi networks / passwords, then it might be cheaper & easier to just use a second router with a different password for it's wifi.

Sometimes old used routers are practically a dime a dozen, definitely much cheaper than buying an new one. An old router that supports OpenWRT / DD-WRT / Tomato would be ideal (but a little more effort to set up).

If you don't want the networks to communicate with each other, then it could be as simple as attaching the new router's WAN port to one of your main router's LAN ports.

Then you could have the children's internet access, or wifi network, or entire router (if it's not the main router) turned off after X o'clock, leaving yours on.

The other answers already cover the "multiple password" part of your question.

Let me give you an alternative, which still covers the problem you're facing:

Parental Control

Depending on your Wi-Fi access point or your router (which may both be the same device), either (or both) may support a feature known as "Parental Control". This can be used to set a schedule during which a specific device may access the internet, or even a maximum usage time (e.g. 3 hours), after which they will lose access to the internet, even if it's not 10pm yet.

If both devices support the feature, I suggest activating it only on one device, preferably the router. Children can get really creative when they want something, and find some way of bypassing the Access Point. There is no bypassing the router, however.

The only downside to Parental Control, is that you need to know either the names or MAC addresses of the devices your children use. If your children managed to purchase a new device in secret, you'd have to block that as well, which you can only do if you monitor your router regularly enough to notice the new device popping up. You can limit this as long as you keep the password secret, forcing your children to go through you whenever they need to connect to the Wi-Fi with a new device. You can use this opportunity to see which new device just connected to the router, and apply Parental Control to it. If your children already know the password, you can simply change it.

EDIT: Re-reading the question, you do not specifically mean wi-fi, but I had assumed this was implied. You may only need a managed switch.

Yes.

• Method 1. Use a separate physical access point (AP), on a different channel.


• Method 2. Create (if router permits) a separate SSID from the same router.


• Method 3. Block their computers by MAC address from your router at scheduled times.


• Method 4. Shape their speed with QOS (quality of service) from your router.

etc.

But. (and, being as nice as I can, this is not Quora)

Your children are capable of using a computer. They will almost certainly work around these measures by tethering to a mobile phone or router. One they may keep secret from you. These are hard to lawfully block (jam). They may even be able to spoof another MAC address to circumvent filtering (or use a "bridge"). They may run a cable from your router, or have their own access point.

So, you needed to have (exclusive) Administration rights to their devices, and restrict their user account logons. This needs to be done at a device level, as your network will not be sophisticated enough to control their accounts.

You can have as many users/passwords as you want by using a radius server and a normal WiFi router (lots of them should support it). This also increases security in general. How to configure this depends on your router. For example if you use openwrt on your router, then it would be explained there.