When wi I be able to tell.........?

When will I be able to tell if the babies I found today are guppies or platties, some have a gray body, some have yellow bodies. Could it be my cherry barbs babies? There is abou 20 of them and I found them today after I got home from summer school - :(. And they were on top of the tank. I think there new born bu maybe a couple days old. So how will I no and when will I no if they are guppy babies, or panda platty babies? Wat color are panda platty babies? Also wat color are gold neon platty babies, blue rainbow baby platties? New born babies that is?