Kangaskhan emerge fully formed from eggs, in their "adult" stage.
Soon after being born, the "adult" Kangaskhan spontaneously creates a clone of itself by parthenogenesis.
The "adult" Kangaskhan can breed normally, and its eggs will generate other "adult" Kangaskhan.
The baby Kangaskhan created by parthenogenesis, however, initially cannot breed, and it grows slowly into the fertile "adult" form, instead of evolving into it. This makes its development more similar to real-world animals than pokémon.
After the baby is big enough to live by itself and leaves the mother's pouch, the mother can then generate another baby by parthenogenesis. This process can happen several times during the Kangaskhan's life.