They are called ‘baby platypus’…  Really, that’s it (officially).  A common misconception is that they are also named ‘puggles’, but this isn’t technically correct.  I mean, you can call something anything you want and because so many people think that’s what they are named, they are often called that, but it isn’t an official name, yet anyways.  Given the pervasiveness of people calling them that, it wouldn’t be surprising at all for them to have the name officially applied at some point.

Although, another common nickname for them is ‘platypup’, so it might win out in the end.  Particularly considering that the name ‘puggle’ is already taken by a few different things, such as a breed of dog that’s a cross between a beagle and a pug; baby spiny anteaters; and a stuffed toy (and yes the name ‘puggle’ is trademarked).

Platypus themselves were named in 1799 from the Latin ‘Platypus anatinus’, meaning “flat-footed, duck-like”.  However, the name ‘platypus’ was already taken, being the name of a certain type of beetle, so their other popular nickname ‘duckbill’ took over and was the commonly accepted name for a while.  Gradually, though, platypus took back over.