If you have children, you are no stranger to knee holes. And if you're still a stranger to knee holes, don't worry! Your kids are probably too young and you'll get your chance.
From my experience, knee holes are the kind of holes my child gets when he plays soccer with his friends and he REALLY has to stop that ball from getting in the goal. So he slides on the ground (or the grass, if I'm lucky) because he simply HAS to, even at the cost of ripping a hole in his pants, right at knee level. And after stopping the ball and saving his team he comes home, and I immediately spot the hole and say "Again??". But no worries there, I just pull out my trusty crochet hook and in no time at all I have the hole all patched and done. This is how it looks from the inside:
