Kids are not supposed to sit in the front seat. Every vehicle I've been in has a large warning label on the sun visor that states that children under 13 (I think) shouldn't sit in the front seat due to the danger caused by the airbag.

I have also seen some vans that allow you to disable the passenger airbag with the ignition key in a keyhole in the dashboard. I don't know if it's safe for kids in that case though.

Here basically all cars can switch off the airbag.

So how do you do it if you drive with your 6 month old? Crying alone in the back? (Of course with two parents one is probably sitting in the back)

If you cannot drive with a kid in the back, you cannot drive at all, because it means your attention is on the kid, not the driving. We had no problem driving with the kid in the back, no matter the age.

In the US you mean? Kid is probably quieter if can see the parent closer.

Some parents might let their ten year old sit in the front, but I have never seen a car seat there, and it's made pretty clear that car seats always go in the back.

In most cars you can reach back and comfort them with one hand, while still keeping your eyes on the road. Otherwise you stop, or let them cry.