Just kidding. I had never heard of one either until about ten minutes ago.
According to the not-necessarily-reliable Wikipedia, monotremes are egg-laying mammals.
Why am I mentioning this? Because baby monotremes are not referred to as cubs. Or mini-monotremes. They're called... You guessed it. PUGGLES!!!!
According to DLTK's learning together:
"A monotreme is a rare sort of mammal found in Australia, Tasmania and New Guinea. The reason they are so rare is that they lay eggs!
This group includes the Platypus and the Echidna (spiny anteater)."