Use Qustodio
Use Qustodio. It works
@Rachaeldv -- I have the same issue, specifically with one device which is an iPhone.
Newer iPhones have an option, initially enabled, to send a "spoofed" MAC-address each time that it connects to your WiFi router. This enhances the device's privacy -- every connection to every different Access Point records a different MAC-address, which makes it difficult to track the "roaming" of the device.
Do your children have iPhones? Are they disconnecting from your WiFi, and then reconnecting to your WiFi, in order to become a "new" (and not-restricted) device on your network?
Login to your router, and get a list of the active connections on your LAN. Repeat a few hours later, to monitor for changes.
@Zapotechelec That is some good advice. I like the fact that this product also controls their access when connecting to another network or when going on data, something that Shaw’s solution would not do.