Are you sure that's a 'he' in the red pants?
We dressed up a little when going to Disneyland in the 1960s, not fancy or formal dress, but not play clothes either, we wanted to look nice. It was a famous place and we knew hundreds or even thousands of people would see us, so we wanted to look presentable. It was exciting to get dressed for it. It was a family event then, not just a casual drop-by for an hour or two. As guests we were part of the cast too.
As for the lack of shade, I'm sure that became evident to the management after 2 summers. The park was brand new so the trees weren't fully grown. By the time I first got there, 10 years after these photos, there was a lot more shade. These photos remind me of how smooth the walkways were back then. I remember Fantasyland as being mainly concrete that had been painted or coated with something and it was as smooth as a roller rink. Now of course, everything is textured, so that nobody slips, falls and sues.
When I find more slides from this day I'll post them. I know there are some more from this day and some from 1965 including my sister on the Flying Saucers, but I haven't found those yet.