Thanks to everyone who has replied to my post. There is so much information to take in. Just to clear a few things up. We are only planning on going to Magic Kingdom for 1 day and Seaworld for 1 day. My Daughter is 4 and I think this will be enough for her,my son is 9 months so won't even know he is there. We are staying on I- drive but hadn't planned on renting a car as we thought the shuttle buses would be sufficient. Can someone recommend a restaurant in the park please and I suppose as I am going in October I should try and reserve a table now??
I'm going to echo the suggestions of others that you sign up for the Mousesavers newsletter and use the Undercover Tourist link for tickets. I just checked their current rates. You can get a weekday pass to Seaworld 1 day for $67 and change. That seems like a good deal. If you're interested in a water park, there's a $37 deal for Sea World's Aquatica. (I'd jump on these; they seemed limited time.). You can also get three days at WDW for $287 and change (a little less for child-- your 4-year-old will need a ticket, not the 9-month-old. As others have mentioned, the President of the United States probably couldn't negotiate a discount on a one-day WDW ticket. Still, I would buy my ticket from WDW ASAP so that I could schedule FPs 30 days out. You can't schedule FPs if you don't have tickets linked to you My Disney Experience account.
I don't know your children and what they can handle, but be advised that Magic Kingdom (which is just one of four WDW parks) is huge-- you could probably spend a whole day on just Fantasyland as a first timer with two kids. Know that you can upgrade your one day ticket to a three day at the guest relations offices at the park. You would just pay the difference. You won't get the Undercover Tourist discount, but that's just $2 on a 3-day pass.
As for your 9-month-old, he will probably be more aware than you think. We took our son at 10 months, and he loved it. The carousel, Mad Tea Party, Many Adventures if Winnie the Pooh, the water play area in Storybook Circus-- he loved them all. Dumbo was his absolute favorite. He also loved pulling himself up on the many rails around the park. I kind of think our WDW trip helped him become an early walker. Check the Disney for families thread in Disboards for more info. My best recommendation is to use the baby center (just off Main Street, labeled on all park maps) liberally. They have great, clean changing tables (better than those in bathrooms), a child's toilet for your 4-year-old, high chairs, a place to heat food and mix formula, and a nursing room.
I'd recommend using one of your non-park days for a character meal. Choose one in a WDW resort, like 1900 Park Fare at Grand Floridian or Cape May Cafe at Beach Club. Character meals can take up to 2 hours, so I would not waste limited park time.
I got to say, I don't think shuttles from I – Drive will be sufficient. The hotels make them seem like they are the solution to your transportation needs, but in reality, the times are very limited. Renting a car will give you flexibility and will allow you to do a lot more with your vacation. Plan to spend some time at downtown Disney, which does not require an admission ticket, and has a lot to do. You can explore Fort Wilderness in Disney World, which has a lot of activities for children like hayrides, an awesome playground, horseback riding, etc. you can even ride the resort monorail, which stops at three Disney hotels and explore the hotels.
My last piece of advice is to download and start exploring the My Disney Experience app. All of the rides, restaurants, and a lot of other park information is there. You can make your restaurant reservations there. You can also schedule your fast passes there. If you don't get the fast passes you want the first time you try, keep trying. I was able to snag and Anna and Elsa fast pass the day we were in the park in May. Also, I wouldn't recommend scheduling your fast passes in the early morning. The lines are pretty short then anyway. Schedule them for a late morning or afternoon.
Have fun.