Size growth after birth seems to be the norm in the animal kingdom (as well as among plants). This makes sense. It's evidently physically challenging for an animal to produce an offspring of its equal size, both if born through gestation or eggs.
But, is this always the case? Are there exceptions, i.e. animals that are born at their "normal", adult size? I don't seem to find any (nor that I am a biologist or expert on the topic).