The point that Tom has raised about the legal nature of AUPs and having children (minors) signing a document is that it is non-enforcable. Dr Brian Bandey (who has written the papers Tom refers to) has been running a closed group in LinkedIn discussing things like this ... and the white papers are available at eSafety in Education | eSafety law | Inappropriate content liability
Well worth a read, both academically and also to help raise the importance of ensuring people understand why you have policies around safeguarding.
Probably because it mentions 'proxy' and so is being categorised as a proxy site.
That's the active content filter that's blocking it. Basically, some of the text on the page is triggering an automated block. I still believe it will be repeated use of the word 'proxy'. If you call SwGFL they should be able to whitelist it for you.