I second what EpcotJunkie says....
we went that time last year. Almost all of the days were shorts and t-shirt weather. A couple of days it was really HOT and humid, and the pool felt wonderful. On our last day, it was cool enough for long pants in the morning but warmed up significantly by afternoon (back to shorts). For my kids, I packed t-shirts, shorts, one pair of long athletic pants, one long-sleeved shirt, one pull-over (old navy type). We barely wore the warmer clothes, but I was glad I had them just in case. We left the heavy coats in Kansas City and were glad we did (no need for them whatsoever) until we got back and it was in the 30's!