I teared up on my first couple visits (which didn't happen until I was 22 years old), but on my third trip in 2004, my sister and I took my 86 year old grandmother, just the three of us, for what was the best trip ever. She was so amazed at everything, she just couldn't believe all that Disney is or does. It was like watching it through a child's eyes. About a month (maybe less) after we got back from that magical trip, she got sick, went into the hospital, then into a nursing home, and passed away all within 5 months. We reinflated her mylar Mickey head balloon for her funeral, and even the preacher at the service mentioned how SHE had mentioned to him how glad she was she went on the trip with us.
Obviously, that next trip I took, I cried when I was in the MK, just all of those magical memories with her welling up.
And now, I've had the joy of taking my now 9-year old little brother twice, and he has become my new Disney-loving partner. Couldn't be happier about that.
So, add all of these emotions with the emotion I felt for Disney from childhood, long before I set foot in a park, and there you have why I am a blubbering mess