Babies sit in carseats, well strapped in and immobile. If you are smart, puppies sit in car-cages. Mine rides in my lap. Babies go in play-pens. Puppies go in cages.
Babies can ride on airliners.
Puppies get shipped as baggage. Puppies can be boarded. Babies are helpless. Puppies can figure out the automatic water bottle and feeder. And the cage door.