How Does Light Slow Down in a Medium, if Photons NEVER Do?

I think any bright curious seven year old might wonder why mysterious LIGHT can pass through SOLID but strangely " transparent GLASS . I suspect that at age seven you even begin to ask the best questions. When I was only seven I recall asking my father : " What is your soul made of ? ". I think I am still wondering about such things ! Still CURIOUS but not much smarter .