Babies go for a walk in a stroller. Puppies, when they will walk, go out on a leash. 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.