Final answer:
Infants and young children should always be seated in the back seat of a vehicle for their safety, as they are vulnerable during development and require proper seating arrangements like car seats.
Step-by-step explanation:
Infants and young children should always ride in the back seat of a vehicle. This is the safest location for them and is crucial for their protection in the event of an accident. Infants, defined as children ages 0 to 2.5, go through significant changes in size and development during this stage. As they progress, infants become toddlers, and by age 4, most children can run, climb stairs, and are often toilet trained. Considering these developmental milestones, it's essential to properly secure them in a car seat appropriate for their age and size in the back seat.