We have taken our five kids to Disney since the first was 15 months. We have always drove and we live 18 hours away. First, stop half way. The kids will need that over night break and so will you. Still to this day I do these thing for at least my 7 year old twins.
1) everyone gets a special bag of goodies...fave candy, chips, fruit snacks, coloring book...etc. Whatever you find that they like.
2) TV TV TV...enough said
3) Stickers and paper.....this was my life saver. Hold on to this until you can't take it anymore. When they are screaming or crying, pull this one out. We would usually make it to Florida before I needed this.
Also, hand over the iphone with fun apps if you have to.