Hi Madison! I tend to be a serious over-packer, so I may not be the best person to give you advice, but my family frequently travels to Walt Disney World around the end of April and beginning of May! It's one of my favorite times to visit because the crowds are relatively light, the weather is usually great, and the beautiful
Flower and Garden Festival is in full swing at Epcot. The average high temperatures at this time of year are in the low to mid-80s, and the lows hover around 60. I generally pack a cardigan or light sweater and some long pants for the evenings, and shorts and t-shirts for the day. Definitely bring your bathing suit because it will be warm enough to swim, but not so hot that you're intensely sweating poolside. Disney is a very casual place so you won't need fancy clothes, although I like to pack a few nicer outfits for dinner. Most importantly, don't forget to bring comfortable shoes because there is a lot of walking at Disney World. (On a trip this summer I had to listen to big Disney Dad Chris whimper like a baby as he limped through the parks because he made the mistake of bringing brand new sneakers, so make sure those shoes are well broken-in before your vacation!)
Hope your first Disney visit is magical! Come see us again at the Moms Panel if you have more questions! We'd love to help you plan your trip!