If the vehicle is a truck that only has the front seat then yes the 8 year old child can sit in the front seat.
But in most states the 8 year old will need to ride in a booster seat that raises the 8 year old child up high enough so that the seat belt fits them properly.
However if the vehicle has a back seat the safest place for the 8 year old is in the back seat and in a booster seat.
Children 12 years old and under should always ride in the back seat which is safest due to the airbags in the front of the vehicle which can kill children 12 and under easily.
If the 8 year old needs to ride in the front seat the airbags should be turned off if possible.
But in some states the law says that all children 12 and under have to ride in the back seat and if they are small enough they must ride in a booster seat or a child car seat.