I have experienced the same thing with my five children and now my grandchildren. It's my opinion that those kids can pick up on the excitement and wonder of places like Disneyland, especially Disneyland though. We have taken ours when they were less than a year old and although they need lots of rest and sleep through a lot of the day, they pick up on the characters, parades and music that fills Disneyland. Our family motto is that we ARE in the happiest place on earth so we WILL be happy. Of course the kids are always happy, it's the adults that most often have to be reminded to just settle down and enjoy the time with the kids.
My two cents.
Thanks everyone for the warm welcome and kind words.
I couldn't decide how to categorize this thread, so I posted it as a trip report because, well, on a basic level, that's what it is. But, I think it's more than that and I hoped it might spark some discussion. I encourage everyone to share their similar experiences here as well. I don't want people to think they are stepping on my trip report by doing so.