chewing on big 3 kids being capable of absolutely devastating natural disasters and apocalypse-level outbursts of power.
Percy who creates hurricanes complete with lightning that pummel titans and flooding and whirlpools that can trap god-powered crocodile kaijus. Earthquakes that erupt volcanoes. Hazel who sunk an entire small island entirely on her own with her final breath, against giants and a primordial goddess of the earth.
If Nico dramatically wilts plants and cracks the ground when he's mildly stressed, and disintegrates enemies down to their skeletons with a single touch or rips their souls out of their still-living bodies, and can command armies of the undead, what happens if he tries to cause destruction? Even outside of total zombie apocalypse or insta-killing a crowd, he's shown enough geokinesis to absolutely be capable of the same destruction Percy and Hazel can manifest.
What about Jason? He can control the winds and storms. There's no way he can't create the most destructive tornadoes with casual effort that he can never justify using for the collateral damage they'd cause. With a single thought he can rip up a town and launch the remnants 50 miles out. (Jason in the center of a Dead Man Walking tornado, vortexes responding to his movements like an avatar...)
And what can anyone do to combat it? How can you fight the wind lifting everything you know and love into the sky, or floods sweeping you away, or the ground giving way beneath you? The Big 3 kids are scary because they are forces of nature, and their whims are the only thing preventing you from witnessing that at any given moment.