I have 3 kids and have taken them to Disney at all different ages and stages from age 1 to my oldest is now 12. I would say the "sweet spot" is really around age 5-7. They are old enough to keep up, out of diapers, mostly done with naps, they still are into the "magic" and the characters, they are tall enough to go on all the rides, they're old enough to remember the trip and they are easier to travel with. I would say a baby (less than about 9 months) is fairly easy (just a lot of work on the primary care givers part), but then a baby who is crawling/cruising/walking to toddler age all the way up through about 3 is probably the most challenging for lots of reasons. Think potty training, nap times, melt downs, screaming, chasing them around, keeping them still and quiet when needed, traveling with them etc. ... it's a lot. Then you get to 3-4 year old's which can be pretty good, but you're still dealing with tantrums and they still get overtired and overstimulated, they aren't tall enough for a lot of rides, yet they "want" to go on everything. If it's a once in a life time trip, I say wait until 5 or close to it. If you plan to go a lot, have at it!