I pick up my niece from school sometimes. I noticed that the parking lot has a gun buster sign. Is it legal to have my firearm with me as long as I do not leave the vehicle? I have my CC permit.

Yes.

You are good to go under Missouri law.

That's only good if it's a Missouri permit, right? I think the law specifies that you need a permit issued by the state in which you live.

Federal law is issued by the state the school is in.  Missouri law doesn't differentiate.

(10) Any higher education institution or elementary or secondary school facility without the consent of the governing body of the higher education institution or a school official or the district school board, unless the person with the concealed carry endorsement or permit is a teacher or administrator of an elementary or secondary school who has been designated by his or her school district as a school protection officer and is carrying a firearm in a school within that district, in which case no consent is required. Possession of a firearm in a vehicle on the premises of any higher education institution or elementary or secondary school facility shall not be a criminal offense so long as the firearm is not removed from the vehicle or brandished while the vehicle is on the premises;

This is the exception to the Gun Free School Zones Act that would apply.

(ii) if the individual possessing the firearm is licensed to do so by the State in which the school zone is located or a political subdivision of the State, and the law of the State or political subdivision requires that, before an individual obtains such a license, the law enforcement authorities of the State or political subdivision verify that the individual is qualified under law to receive the license;

So, in other words you must have a Missouri CCW license and you won't be breaking federal law.

I am not a lawyer...  If you want a definitive answer, contact one.

Thanks lambo, that's what I was thinking it said. Since I have a FL permit, I left my gun at home when I went to my sons school. He's out of school now, so no more worries for me.