I am an adult, and a reasonably happy one at that; I feel I have a lot going for me. Though certain aspects of the world around have a tendency to piss me off, I'm not depressed, and I generally have a positive opinion about my own life.
That being said, I do not want my kids to grow up.
Some parents wish for this because they don't want to lose the cuteness and
innocence of a baby or a very young child, and I completely understand that
perspective. I mostly didn't care about any babies before I became a father and
now I'm smitten with my own and can appreciate the offspring of others.
However, this is not why I want my kids to stay young. I want that for them
because I've never seen any adult get so happy and/or excited about the simplest
things. You might ask then, why not just wish for them to keep that perspective
as they age, but if as an adult they still had the same amazing sense of wonder,
someone would probably think there is something wrong with them.