We've been to Disney twice in June and four times in October. The first week of June is not summer crowded, as a significant number US schools aren't out yet on summer break. Early October is much more crowded than late October, when crowds ease off a bit. Fall breaks tend to be in early October, and Columbus Day, which is the same day as Canadian Thanksgiving, makes things more crowded. Complicating matters in October are MNSSHP, which really restricts hours at the MK and in turn pushes evening crowds to other parks, mainly Epcot since Food & Wine is going on. Early October whether may not be substantially different than June...one of our trips, it was in the 90s every single day.
We started going to Disney when my kids were young (2 and 5 on the first trip), and now that they've aged 5 years and can stay up later, I find we're appreciating the summer hours more, because we all trend to being night owls rather than early birds.