This is a question that I often answer and many can agree or disagree with me but I speak from experience!
My own children visited when they were under one year age and it was mainly because we had family reunions and I wasn't going to leave them behind. As the years went by I realized how important those earlier years of Disney were to my children and also to me. My daughter had not smiled much as an infant until I took her into the Tiki Bird attraction at 11 months of age. She started laughing and has never stopped! I will never forget that moment and many others.
My best advice is not to try to find that "perfect" age for children to enjoy themselves at Disney. There isn't one! What memory of your children's reactions and actions will prove to be more special then the others? With every visit they will grow and learn and have fun as you will. You will cherish every picture and later will share with your grandchildren the good times even if they don't remember them. I will never forget taking my grandson when he was about 18 months and watching him jump right along side of Tigger at a character meet and greet. The excitement on his face was priceless!
So with that said, you and your family can have a fabulous and magical vacation with any age child as long as you go with the right frame of mind. Don't' try to see every attraction and gear the trip to what all of you can enjoy together as a family. Make the trip easy on yourselves by shipping boxes of baby necessities to your resort or use one of the great grocery deliver services that will deliver to your resort for your arrival date. (
www.gardengrocer.com) Keep things as stress free as possible and if you enjoy yourselves the children will also no matter what their age!