We live in Calif. and have been to
Disneyland lots of times (only been to WDW once but are going to fix that in December)! We've never been during Mickey's Halloween Treat, but have been in the fall. The weather in a few weeks will probably still be fairly warm (but not as warm as Florida!) with cool mornings and nights. We don't get the humidity that FL has so even warmer days are still comfortable. You'll probably want to start out with a sweatshirt in the mornings and then wear it again in the evenings. I can recall spending a long day there one October and wearing jeans and a t-shirt and keeping a light jacket in a locker. I would recommend watching the weather reports as your trip gets closer since rain and colder weather in October is not unheard of. I can safely say that, in general, October tends to be on the warm side.
As for your 1-year old, DL has its own Toon Town that is very colorful. There's a fun little area with sound effects and silly things to try. DL has many of the same rides as MK and a few MK doesn't have. My kids love the Casey Jr. Circus train - they're 11 & 8 now but they loved is as toddlers and preschoolers too. Winnie the Pooh or any other rides with familiar characters are also a good bet for little ones.
Hope you enjoy your trip!