It is illegal to have a rear facing child car seat in the front seat if the air bag is active. This is because when the airbag is deployed it comes out at a very high speed; if that were to hit the back of your child’s car seat the consequences would be devastating. If you want your child to be in the front with you then make sure the air bag is turned off, some cars have to go to the manufacturer; on others you can do it yourself. You should also push the front seat back as far away from the dash board as possible, as when in the front seat the child is being put closer to the force of the impact.
There is no law regarding deactivation of the airbag when a child is forward facing in the front of a vehicle, however you must check your vehicle manual to see if the airbag must be switched off and positioning of the front seat. Some vehicles do not allow a child under 12 years or less than 135cm in the front of the car - so it is very important to check the car manual. The information will be in the child seat section.
I have shared this, because this is something that is asked a lot especially among mums on FB and forums.
Maybe now they will take my word for it with this link.