but I want to ask, is really advisable for one to keep ones desires and aspirations of tender age up till grown up. Because I believe when u are still young there are a lot of things we don't understand until we grow up.

I used that as an instance. However, kids have an innocent mind that believes everything is possible, but as they grow up, the world begins to tell them what is achievable and what is not (although they are wrong most times) and begins to plant some good and evil seeds in them.

Holding on to one's childhood dreams cannot be said to be good or bad.