I'm planning 2 days with my 6 year old Dr, but we don't do full park days, it's usually morning until he's starting to get rid of needing a change, which is usually sometime mid to late afternoon. So my plan is to do FW one day and WS the second day.
That being said, I do think you could get a lot covered in 1 day and leave the 2nd for Sea World.
I've read mixed opinions about whether or not to do World Showcase at all with my young kids. I would love your opinions. I'm leaving 5/2 and I've got to figure this out today!!

With the ages of your kids I would plan on doing 1 day in Epcot. We spend a lot of time walking in each of the countries but I think a 3.5 year old and a 6 year old would probably not enjoy that as much as they would sea world.

...But at that age, my kids really liked Sea World too. Good Luck, we will be there a few days overlapping, fingers crossed for dry weather!![]()