Superman Hulk who would win
To be honest, I think this would be a bit of a curbstomp. Superman on his own could likely take down the PPG on his own, as he is ludicrously overpowered. He has incredible durability, far surpassing what the PPG displayed in the show, having survived multiple supernovae to the face, he regularly goes at lightspeed, and his far superior intellect means he would outplan and outfight them at every turn. His powers simply outstrip each of theirs, easily.
Thor is not as overpowered as Superman, but would still put up a hell of a fight. He's very durable, extremely strong, and has lighting to work with. I'd think he'd be unable to hit the PPG with his hammer, as they're small, fast targets and his hammer would be relatively slow, but he'd be very difficult for them to defeat on his own.
Hulk, provided enough initial anger, would be a pain in the ass for the PPG. He's practically invincible, provided he's got enough rage to build off, he's superstrong, and so on. Theoretically, his powers have no upper ceiling, so the longer the fight goes on, the bigger his advantage is in the fight. Hulk would be a threat solely due to collateral damage, however.
Superman, Thor, and Hulk together would honestly wreck the PPG, if only because of fighting experience and skill, on the part of Superman and Thor, and on account of the sheer unstoppability of Hulk. Superman and Thor are both much more intelligent and experienced in battle than the trio of young children could possibly be, and their superior strategy and superior powers would easily net them a victory in such a conflict.
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