Dreams don't get stored in long-term memory unless you make an effort to think about them. They are very easily lost, which is why you can feel them slipping away sometimes just as you are trying to think about them. However, if you do manage to think about a dream and concentrate on it before it is gone, you can remember it, and then it is just like any other memory. You probably thought a lot about those childhood dreams after you woke up, and got them permanently stored in your brain.