Hi Zulimar! October is a great month for a Walt Disney World vacation. The weather is starting to break and give some cool relief from the heat and humidity of summer and the holidays are geared up and in force in the parks.
Since you have four day passes you would be able to enjoy each of the parks for one day. Each park includes many great attractions for all age levels. Obviously, the best park to enjoy with children is the
Magic Kingdom. This park is full of magic and pixie dust and seeing the castle for the first time will be a memory you will never forget with your children. There are tons of character meet and greets everywhere and the most attractions of all the parks so you could easily spend two days in this park.
My second choice for children is the
Animal Kingdom Park as what child does not enjoy seeing and experiencing animals. The Safari ride is amazing and my all time favorite show is the Lion King held throughout the day in its own theater setting. Children of all ages will be mesmerized by the singing and dancing for the 30 minute show. Rafiki's Planet Watch is another spot not to be missed. Take the train to this outpost where the kids can pet and brush the resident goats and sheep as well as see other animals. They often have something exotic out that they can learn about and touch.
Hollywood Studios and Epcot are awesome parks but they do include more of the thrill rides and your eight year old might not reach the height requirement for some of those. If you have a park hopper ticket you could easily enjoy both of these parks in one day as they are connected by a water taxi making it easy to go from one to another.
My vote for Halloween is the Magic Kingdom but know it will close at 7pm for the special event, Mickey's Not So Scary Halloween.