Is it common for race car drivers to start in kart racing?

Pretty much all Formula 1 drivers have started in kart. An F1 car is just a big kart that costs a few hundred million $.

At the higher level, pretty much all of them did. They've usually been racing since they were four or five.

Very common, at least, I'd say.

Yes, pretty much every modern F1 driver started in karting.