<Snipped quote by Memory>
Kangaroos don't really have a lot of babies at once like many animals. And those that are genetically related to them, Marsupials, have evolved to carry their young with them even after birth. Its a type of evolution change that allows for a higher chance of their babies to survive.
*starts drawing dogs of different breeds*
Most animals actually have multiple babies at once, they are very tiny though. Like these dogs. Some get pretty big, like to my belly, but most are smaller than waist height. These animals are typically companions or pets to us.
All of the ones with a bunch of kids are pets?