We've been using Zenni Optical for about 3 years now. It was for Adrian and I solely but now our little guy has had to join us. He was a little nervous about it all at first but after looking through their selections for kids, he was much more excited about the whole process.
I received some other mom advise from friends with kids in glasses. They told me that a big deal will be let them choose what they want. And believe you me...he did! Needless to say, he loves them!