Book a hotel close to Disney park (better in the Disney campus if you can afford it).
Get in as early as possible. Do the attractions with least people in lines first. Take advantage of Fast Pass.
For Magic Kingdom, take your kids back to hotel to take a nap around 3:00pm or 4:00pm, then have a good dinner. After that, go back to Magic Kingdom and enjoy the night till midnight when they'll do a night parade and fireworks show.