Kids belong in a back seat until 12-13 years old.
http://www.car-seat.org
References :

Do air bags pose a danger to children?
Yes. Front air bags have been required in all passenger cars since 1997 and all SUVs, pickups, and vans since 1998 because they save lives — but as of June 2007, they had also killed at least 180 children, several of them infants in rear-facing seats. Some of those deaths occurred in what should have been mere fender-benders.

What makes them so dangerous?
Air bags inflate almost instantly after a crash, often bursting from the dashboard at 200 miles per hour — more than the force of a heavyweight fighter’s knockout punch. That impact can injure or kill children and even adults who are seated too close to the air bag or are thrown toward the dashboard during emergency braking.

Never place a baby in a rear-facing seat in the front seat of a car with an active air bag. The seat positions their head so close to the dash that they’re directly in the air bag’s line of fire.

Air bags can also be deadly to older children in the front seat. Because children have weaker back, neck, and stomach muscles, and because their head is larger in relation to the size of their body, it’s harder for them to maintain an upright position even in a gentle collision. So they’re more likely to come face to face with the blunt force of the bag as it expands.

Where’s the safest place for my child to sit?
Ideally? The safest place for anyone (including adults!) is the middle of the backseat, or of the center seat in a van or station wagon. But if more than one child is riding in the car, only one can occupy that spot. And if the center backseat has no shoulder belt to secure a child in a booster seat or an older child, it may not be suitable.

In general, kids age 12 and under should sit somewhere in the backseat, using the appropriate child or booster seat or safety belt for their age and size.

What if I have to put a child in the front seat?
If you’re forced to seat a child up front because the car is full car or it lacks a backseat (a pickup truck, for instance), slide the seat as far back as possible before installing the appropriate child safety seat or booster. If the air bag has an on-off switch, set it to "off." If you can’t turn the air bag off, under no circumstances place a rear-facing infant car seat in that spot.

If you don’t have an air bag on-off switch and regularly need to put a child in the front seat, consider getting a switch installed. You can find out how from the National Highway Transportation Safety Administration (NHTSA).
References :
http://www.babycenter.com/0_car-seat-safety-air-bags_396.bc