According to Just Drive PA, it is strongly recommended that only children over 13 years of age should ride in the front passenger seat. The expulsion of a passenger-side airbag is too much of a risk for small children.
Children under 13 are often not large enough to safely withstand the impact of an airbag. Just Drive PA states that children from birth to 12 months are required to ride in a rear-facing car seat. Children 1 to 3 years of age are required to stay in a rear-facing seat until they meet the weight limit allowed by the seat's manufacturer. Children 4 to 7 years of age are required to ride in a forward-facing car seat until they meet the weight limit set by the car seat's manufacturer. Children 8 to 12 years of age are required to remain in a booster seat until they are large enough to properly wear a seat belt.