Judging by their attitudes/actions in their respective episodes, I reckon Q would make short work of Trelane, even though Trelane may in fact be his forefather. Trelane certainly had his fair share of power and dangerousness, but technically he was a child - clumsy, easily manipulated, and not quite fully confident and in control of his own potential force. Q, on the other hand, was completely sure of himself and therefore, a much more formidable adversary, and it usually took considerably more complicated thinking and/or action on the part of the crew to defeat him than it did Trelane.
Trelane is just a kid and doesn't demonstrate nearly as much power as we've seen from Q. Q would win hands down!
Gagh! Trelane my ass! "The Squireo of Gothos" was simply ridiculous. Never liked that episode. No wonder Futurama made fun of it. Q rules!
Q. Q seems older and much more ruthless (especially early on in TNG). Trelane was more immature and child-like. His abilities also seemed to be limited due to the boundaries set forth by his parents. Q didn't appear to have many boundaries placed on him by the Q Continuum.
Didn't Trelane rely on some sort of physical instrumentality that Kirk was able to screw with? Now we know from VOY that Qs do as well, but it seems far more robust and removed, and hence difficult/impossible to sabotage.
There was a comic about a duel between Q and Telane, which I have in my possession. Here's the first page (sorry about the quality, but that's because I compressed it to less than 100 kb):
If anyone read the book "Q-Squared" you should have your answer. From what I remember Q was more of an Uncle to Trelane?? But I read that book a lond time ago, so I'm probably wrong. besides Trelane used a machine to create his 'illusions', Q does not.