I swear they do it on purpose. They have several techniques.
Sometimes they work together on their timing. One will look at the camera and the other looks away...
and then they swap and the 2nd one looks while the 1st one tries to fall out of the chair.
And then there's always the tried and true "Saboteur" route
And when all else fails, just sit there and cry!
Thank goodness for Photoshop and the ability to "Frankenstein" a picture! (Take one kid or head from one pic and stick it in another) Otherwise I'd never get cute pics like this!
And while it's not great, it'll have to do, cuz that's as good as it gets with these two!