Same thing happened to my fiancés coworkers kid. The pipe sucked his arm in and got his head under water. They couldn't get him out so they needed to wait until all water from the pool was drained. It was their only kid and already 12 or so.
Damn. I was hoping you would t say that. As a dad myself, I could t think of know a worse thing to happen — especially since one of my greatest fears is to die via drowning or suffocation. That breaks my heart for that family.
My guess would be that the first attempt to rescue would usually be to turn off the filter and / or attempt to jump in and pull them out. I would think by the point anyone would think of and be able to access something to breathe through it would be too late.