My DS (now 6) got his first pair of glasses when he had just turned 3. His vision is so bad that it only took a day for him to realize that he could see so much better with them on. We took it slow the first day and didn't get too stressed when he took them off a lot. By the second day he was more ready to give them a chance.
You got good advice, go to a place that has a good replacement policy and good hours. We have made many trips for new nose pieces, adjustments, and new frames. We get our DS's frames replaced for 2 years for any reason.
There are so many options and a lot nice frames out there for kids today, so much better than 20-30 years ago.
Good luck!