Hi Donna!
It always takes our family (family of 4, children 6 and 2) two days to do Magic Kingdom. Not only is it massive, but if you catch any of the shows, parades, eating around the park, etc., it's hard to pull it off in 1 day for us. Also, you have to get as far from Main Street as you can if you don't want to watch a parade. When any of the parades start, that whole walking area from Main Street up to Cinderella's Castle shuts down, and you pretty much have to wait till it's over, and the crowds have disbursed, just to get around.
So I'd set aside 2 days for Magic Kingdom, 1 day for the remaining parks...
Good Luck with your planning! Your vacation is just around the corner!