The scene indicates that you are using a rationale or logical way of thinking (the van) that is very important in your mind but also reflects much innocence as well as a worldly level of truth. (a large white van) The presence of innocence or naiveté is also emphasized by the children in the van. The van also suggests a way of thinking that really "works" and might even relate to a work situation.
The key would represent the permission or the right you have to use the rationale being used. When you cease using the rationale or idea you have been using (park the car) by cutting out the motivation for it (turn off the ignition) the permission to use this rationale no longer appears whole, wholesome or positive. (key broke) Finding another whole key in your hand would imply that in your own mind, you might be finding it impossible to break with the permission or the right you thought you had to use your way of thinking about an issue. The idea still looks positive in your mind.
Having another key - implying a second key - indicates that the permission to use your rationale that had seemed quite workable can now be considered as being negative rather than positive. The motivation for using your way of thinking seems blocked by the idea that the permission or right to use the rationale is really not wholesome, positive or good. (broken key is stuck in the ignition)
You seem unable to get out of a situation involving the rationale you have been using. You seem to be "in a jam", in a troublesome position. There may be many issues keeping you in a situation. People often speak of debt "piling up".