This is the best reason to buy a new bike and sell it. Brand new last week but it's a 2018?
Late to the party on this reply, I know, but I saw a 2018 Anthem 29er for sale in a shop a couple of weeks ago. It was alloy, not a carbon Advanced, but I'm sure there's a few more out there.
Selling because he can't tow a trailer? Hmmm, the Robert Axle Project exists:
https://robertaxleproject.com/cargo-child-trailers/ Perhaps he didn't bother to look for a solution, or he's just decided that towing on an Anthem Advanced isn't recommended (vs not possible.) Or lying / idiot. Price seems a little high, if you did find one in a shop you could probably haggle them close to his asking.
I towed a single-seater Chariot a 26" Anthem a few times without drama, including a lap of stromlo firetrails (using custom wheels with 24x2.3" tyres..)
Also for a year or so with a carbon CX bike, it has a 10mm thru axle and the pulling on the axle on the non-drive side apparently made the axle threads on the drive-side slowly eat into the front face of the dropout, making the wheel out of alignment. Should have tried to convert the hub to QR to stop it but not enough tuits .. the threads are probably still eating into the top of the dropout now, come to think of it. Fixed it by buying a steel tourer with QR rear hub, for two-seater Chariot towing + racks.
also LTIL: Norco making proper trail bikes for kids, modern geo, real air suspension, for reasonable prices:
https://www.norco.com/bikes/2020/youth/youth-trail/ Well, Yes, those are all a lot of money for a 20/24" kids bike, but they're all a decent price for the spec. And cheaper than the very few other brands doing it.