Boy, I sure wish there was an easy way to tell as well!
When I first started looking for a yorkie, I went to a womans house and she had 3 females that she showed me and was trying to talk me into showing and I wasn't sure if that's what I wanted at the time. Anyways, she showed me one and said see, this one is going to have a soft coat but these other 2 are silky. They were about 6 months old at the time. I couldn't see the difference. I just sorta shook my head and inside I was thinking they all looked the same. Now I can tell the difference when they are grown but wish I had a little more experience with predicting how things are going to turn out!