I went with my six year old granddaughter and her mother as her mother had never bought specs before. Optical Express were really good, but did not have the sort of frames she wanted.
We went to Boots, and they realised that none of their frames were small enough for grand daughter, after trying some on. Then we went to Specsavers. We were told to look at the frames and let them know if there were any we wanted. No advice at all, which we could have done with for a six year old. So we went back to Optical Express, as we knew they had frames that would fit, even though they were not Peppa Pig!