What you’ve described is perfectly understandable, you don’t need complex language to understand what you are trying to achieve.
Unfortunately the method you’re using to block access to porn sites isn’t ideal, and the youngsters will find ways round it. This Meraki document, https://documentation.meraki.com/MR/Firewall_and_Traffic_Shaping/Adult_Content_Filtering_Overview goes a little way to explain this, and highlights that it’s not an ideal solution. If you have a list of HTTP hostnames you want to block then you could do this on the Firewall for the SSID using the Layer 7 firewall capabilities https://documentation.meraki.com/MR/Firewall_and_Traffic_Shaping/MR_Firewall_Rules. You will have to configure these per site. The thing to remember is that this is still a very static solution, and you’ll have to continue to monitor and update the outcomes.
Ideally, although it does come at a price - which may or may not be feasible, you’d want an automated solution. One such solution could be Cisco Umbrella which integrates with the Meraki MR devices and provides continually updated categories, and is good for malware protection too. The other option is to look at using the Meraki MX security appliances (with the advanced security license) which provide a more comprehensive content filtering solution.
I’d suggest it’s probably worth getting in contact with your local Cisco/Meraki team, or reseller, and see what they may be able to do to assist.