How do you get infant dogz out on dogz 5

Get a dog pregnant and wait for the offspring. It takes 3-6 days. Exactly the same in Catz 5 too, if you have it. In both Petz 5 games they have a nursery.
In Petz 4 you only get one baby and it can enter any room (apart from the Adoption Centre, obviously). Remember not to spray, scare or "Watering Can" the babies, it crashes the game, and (in petz 4), don't snowball or take them to the beach/south seas, cause the water splashes them.