The Magic Kingdom will hold the most rides and attractions for children those ages, so I would plan to spend the majority of my time there.I'm not sure if you are spending entire days in the parks, or just going in the evenings after your work event, but it is a very large, two-full-day-park. If you only have evenings, you might want to allow several of them in order to see and do more there.
Animal Kingdom is my own children's second choice, followed by Hollywood Studios and then Epcot. This is primarily because of your kids' young ages. Epcot, while wonderful, holds the least to entertain little ones.
October is a really great time of year to visit! The weather is lovely, and the fall decorations are up and very festive. If you'd like a special event,
Mickey's Not So Scary Halloween Party would be a blast! The kids can wear their favorite costumes and spend a night trick-or-treating in the park, with special holiday themed shows, parade, and even fireworks. This is a must-do for my family.
Also, I strongly suggest that you either bring or rent a double stroller. Even if your children generally walk at home, they will be exhausted at Disney. It's not uncommon for us to walk 10 miles a day in the parks - far more than most little ones can handle!
Good luck!