Okay, here's what you do...and please keep in mind that this is not an easy task to begin with, and it's 58 times harder when they are young. Gently cup the hamster in one hand, and sort of flip it over into the other, of course holding gently but firmly. Sit on the floor so that if you drop a baby, it will not hurt him or her, and that he/she'll fall from a very short distance into your lap. Have a good source of light available so you can see. Try to spread the fur down there enough to see their "openings." Have 2 cages or enclosures already set up prior to doing this...one for your girlies, and the other for your lads.
A male will have two distinct openings...it will sort of look like an exclamation point, or an "!" The anus will be slightly further down. A female's vaginal/anal opening will be close together, or it will look like one opening...or an "x". Somewhere on the internet, there will be diagrams for dwarf hamsters...try www.hamsterhouse.com
Also, in more mature male dwarfies, you can often see the testicles...they'll look like little pom-poms protruding from the bum. I find that females often have slightly rounder little bodies, and the males are often more enlongated.
Mistakes in sexing dwarfies happen. It's hard for the typical layperson to do, and sometimes even for vets. Do the best you can, and get them separated in the next couple of weeks, if at all possible!