Platies, swordtails, mollies, guppies etc are livebearers and will give birth to live young. The females also have the capability of storing sperm and using it for a later date. Therefore, it is possible for a female to have up to 8 lots of babies from a single mating !!!....that is why they always seem pregnant.
unfortunately, the babies will stand very little chance of surviving in a community aquarium unless it was heavily planted with both low growing and floating plants. Good luck though.