we only did disney once and that was enough misery for me but we do still enjoy going to Florida but stay away from Disney. Universal Studios is so much better, we also enjoyed Busch Gardens, Gator Land, Sea World, and going to the beach.
In Missouri, St Louis is great with all kinds of activities. The zoo, Science Center, and Grants Farm are free, can go to the Arch, Cardinals game, or Six Flaggs (probably not open in the spring). Branson is also fun with all kinds of different things to do.
If you really like amusement parks. Cedar Point is the best park ever. It is in Sandusky Ohio, has 17 awesome roller coasters, an awesome water park and is right next to Lake Erie. If you live in the KC area, I recommend buying the 160/person passport at World's of Fun/Oceans of Fun, this pass is a park hopper and can go to all their parks in the country. We did this for vacation last year, went to Cincinatti Ohio to Kings Island first, then drove on up to Sandusky and spent 3 days at Cedar Point as it takes more than 1 day to ride everything. We plan to do this trip again next year because the kids loved it so much. With the passport you get unlimited entrance to all the parks they own, get to enter the park earlier than it opens and hit the lines quicker, free parking, discounts on some food places in the park, but we usually leave the park and eat at a restaurant and go back. You can check out their website at www.cedarfair.com plus you get to go unlimited here in KC to Worlds of Fun and Oceans of Fun. Since you are talking about Spring break you may want to check on the dates first as they may not be open that early in the year.
If you do decide on Mexico, you will need a passport for each person. You want to apply for them 4-6 months in advance as they take several months to get them back. My son went to Haiti on a missions trip. He was leaving the end of July, I applied for his passport in February and we were worried he wasn't going to get his passport in time, it came through a week before he left. They cost over 100.00 each.
Hawaii would probably be cheaper and you won't need a passport. My brother and his family went with their 2 little girls last year, they loved it and want to go back.