Happy are they who still love something they loved in the nursery: They have not been broken in two by time; they are not two persons, but one, and they have saved not only their souls but their lives. -G.K. Chesterton
The idea of keeping the child alive in my spirit is a very important one to me. When I look around at the adults with whom I have a lot of contact, one of the things that I see regularly is that those people who are letting life bring them down tend to also be the people who don't have the ability to see the magic and wonder of the world, those people who show absolutely no indication at all that they've actually been children. They've fully and completely "grown up," and they're now serious people who have nothing to do with the things that children love.
But as children, we loved more purely--until a certain point, we were able to love things just as they were, not for what we could get out of them. That point was different for each of us, that point at which we started to love things for the benefits they could bring us. Those benefits could have been status, other people's admiration, money, clothing, or whatever--we learned that the world wasn't magic, that it was something we could manipulate for our own good. And we stopped seeing the world as a magical place once we decided to use the world to help us to "get ahead," which in reality was actually falling behind.
That's why it's so important that we pay attention to that part of us that was a kid--so that we don't fall behind any further, so that we continue to be able to love things purely for what they are, not for any benefit they can provide for us.
The adult doesn't have to be a different person than the kid was--there are many, many aspects of ourselves when we were kids that can help us to be happier and healthier people. When we were kids we were more easily satisfied and we didn't think nearly as much about what other people thought about us, and both of those traits are generally regarded as traits of people who tend to be happier than others. I'm sure you can come up with more of them. And that kid is still an important part of you--perhaps it's time that you uncovered that child that you were and allowed him or her to see the world and revel in its wonder and magic, instead of constantly seeing the world through jaded and disillusioned eyes. Let the kid do the seeing for you, and you'll be amazed at how beautiful the world and everything in it can be.
And an important first step may be to love something from the nursery again, be it a stuffed animal, a bouncing ball, a favorite toy, or anything else that elicited sincere, loving feelings. Don't allow it to remain buried under the years of crud that other adults told you was important. Your life and your happiness are too important for you to allow that child to remain out of your life--bring him or her back into your life, and enjoy his or her company!