Mollies and Guppies will breed, So if the molly is female expect babies,
First off if you don't want babies you need to find out for sure what you have, males and female wise,
Male guppies are very active all the time, It's one of the many reasons they are so popular.
An all male tank is beautiful to watch, very entertaining and colorful.
If it'll make it easier for you to determine what you have, Heres a link to some pictures I posted of a male and female, Highlighting the sexual difference, This holds the same for Mollies, platies, swordtails and guppies,
Sextons Aquariums - male or female