all of the parks are good for your age group!
Your 2 and 6 yr old will love the safari at AK and it's tough to be a bug will really thrill your 6 yr old plus the petting zoo and perhaps the lion king. Also the afternoon parade and character greeting in camp minnie mickey.
At mgm you have all of the great shows such as the little mermaid, playhouse disney and beauty and the beast also muppet vision 3D. You have the parade called stars and motor cars also.
Magic Kingdom is your best bet with Mickeys Philharmagic, Its a small world, peter pan. The pirates of the carribean and Haunted mansion will be good for your six year old but not so much for your 2 yr old if he/she is easily affraid my 18 mos old was not at all affraid but I think she was to young to be affraid. Buzzlight year will be fun. Jungle cruise, pooh, and the wonderful parade called spectro magic. Take them to toon town fair and get autographs with there favorite characters. MK has a lot to offer young children.
Epcot has kidcot funstops, turtle time with crush, Honey I shrunk the audience it's 3d, Figment they may like visiting the countries. Mexico has a neat ride and Norway. Inside the big "golf ball" is a classic ride called spaceship earth that is fun.
As far as times go most people recommend getting into the parks early as possible. Fast pass certainly helps with attractions that have long lines and riding during parade times also helps. allear.net has a list of all the parks and there attractions and characters it is a great resource. Have fun!
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