Get all your children Equity cards..
"..The Classwatch website also focuses heavily on the issues of staff development and teacher support, both valid uses for in-class recording..."
As there seems to be a bit of a legal fudge going on somewhere as to the 'public place' status of schools/classrooms, and, bear in mind, schools get stroppy if pupils or parents try filming on their grounds..
Ok, so get your kiddies onto the books of an acting agency, once the cameras are rolling, as pushy showbiz type parents (or, better still, get your new star's agent onto them), you could argue the case that, as the wee red light is flashing, your darling child is no longer being educated, but is participating in the shoot of a "staff development " video, or is participating in some other form of ertzatz "reality tv" type recording, then demand that they get paid the appropriate equity/whatever hourly rates for child extras, and, ISTR, the rates are higher if you have a speaking part.
Claim copyright abuse over unauthorised use of actor's image, demand all video footage etc in violation be turned over to you..
Screw with them, skew their CBA to the point that they'll see it'll cost them dearly to keep the cameras in place. They're supposed to be running schools, not Stazi detention and interrogation centres.
(and yes, I know Equity cards are now no longer strictly required for luvvies etc)