It is fun to pretend animals could be different than they are. Unfortunately, if we made the changes shown here the animals would not be happy.
Giraffes come from Africa where it is hot and dry. They are the tallest animals on land, some growing to 18 feet. They are related to deer. Over millions of years they evolved long legs and necks. This allows them to eat leaves from very tall trees. With short necks they would have to find leaves on bushes, now eaten by other animals. If they could not find enough short bushes they would go hungry. Having to carry their babies in a pouch would make them slow, easy prey for lions.
Kangaroos live in Australia, and are marsupials with powerful hind legs that let them jump very far. Marsupials give birth to tiny babies which must stay close to their mothers, such as being in a pouch. Without a pouch the babies would not be safe. Having a long neck would make jumping very awkward. They are better off the way they are.