I think the concept of Q+ raises different questions in children than it does in adults.
In adults, the best summary for me was during the LGB Alliance tribunal hearing, where the witnesses from LGB Alliance articulated very clearly why they are concerned about the Q+. Queer is a word that many older lesbian and gay people still see as a homophobic slur, and the + could mean anything. They were treated as bigoted and hysterical for questioning whether it could include things such as bestiality and paedophilia, but the point is no one is actually willing to stand up and say what it does and does not include. It's a miscellaneous category. Who wants their equal rights movement to include a miscellaneous category of people whose motivations and needs are unclear? And it obviously isn't so much of a stretch to imagine that the + might include paedophilia, since Mermaids appointed a man who had published written material about his sexual desire for children and addressed "minor attracted persons" at a conference. If nothing else we know that Pride has been expanded to include a lot of people who display their sexual proclivities, as opposed to their sexual orientations, in public. Although these things are perfectly legal, many gay and lesbian people do not want to be associated with them because they have spent decades telling the world that they aren't sexual perverts, they're completely normal people who just happen to want same sex relationships.
I think adding the T to the LGB was already a stretch, given that T means anyone who believes they have a gender identity which does not correspond to their birth sex, whereas LGB just means same sex attracted. Two completely different things. But then you add on the Q+ and it's unclear who this group actually is, apart from straight people who prefer not to identify as straight, such as Laurie Penny, and potentially shady people like Jacob Breslow.
I don't think a lot of these concerns necessarily apply to school age children. Due to the ubiquitous nature of online porn, unfortunately all children may be exposed to ideas and material of a sexual nature, some more mainstream than others, and that is the case whether they identify as gay, straight, trans or whatever. Children are unlikely to recognise queer as a slur, due to their young age. But given that LGB already covers same sex attraction, and T covers trans and non binary gender identities, what is Q? What makes children who identify as Q different in any way from children who are straight?
This club specifically is already open to "allies". So why not LGBT and allies? What on earth is the Q+ when you are talking about children?
The only thing I can think of is that the Q+ is for children who are not same sex attracted and do not identify as trans or non binary, but want to have an alphabet letter for themselves anyway because it is currently deeply uncool to be "cishet". This is essentially the Laurie Penny category, only she is old enough to know better.
That's a very long winded way of saying I think the use of "Q+" among teenagers specifically is not a sign of trying to sneak paraphilias in under the LGBT umbrella, which is what the LGB Alliance are concerned about in adults, but it probably is evidence of social contagion, where even perfectly ordinary children now feel pressured to identify as anything other than a boring straight person without a specific gender identity.