Yes. The 6-year-old should be in a child safety seat in the back yard. Probably the 8 year old should be as well.
Its not the fine that you should worry about but the welfare of the child.
A 9 year old child can ride in the front seat of a car. It is important that they are buckled in and can sit still.
A six year old can be placed in the front seat but they must use a booster seat if they are under 135cm tall. Under no circumstances should a rear facing booster seat be used in the front seat.
With a car seat to boost them up, Yes.
A 5'7" child can't fit in a child safety seat. Many adults are 5'7".
it is true that you should not use an infants car seat if they are over five they should then be moved on to a booster seat .
Whether or not your 12-year-old needs a booster seat in the car depends upon the laws of your state. Each state seems to have different rules about age/weight/height requirements.
no
no they have to be 13 and older
no ma'am ___ No, it is unsafe and illegal. You can, and will, get a ticket if you are caught doing so.
By 8 years old, the child should be old enough to sit in the back seat without a booster of any sort. If you are concerned as to whether he is allowed legally to sit in the front seat you can test if his head reaches above the seat he SHOULD be allowed but to double on that you might want to check online in your country for a legal age :)