Ok guys. I'm a newer DM (only about 8-10 sessions total) my party consists of 5 players. I have no problem handling the size of the party, the main issue I have is the lack of seriousness of the party. I understand that DnD isn't supposed all serious all the time and that it's about having fun, however even in the most dire situations with the most important NPCs they continue to goof off and not take anything seriously. Perfect example, last night we made it to the capitol city on a very important delivery mission to the local wizards. As they were approaching the wizards tower there was a stainded glass window on it, on of the members said they wanted to throw a rock through the window to break it. Then, when the party approached the wizards, the party sorcerer did what he always does and casts prestidigitation on one of the wizards to make him smell like garbage. (This is something this sorcerer does on a very regular basis, he doesn't use that spell for anything other than to make people small like crap, literally.)

TL;DR My party is a bunch of immature turds who can't take even the most serious situations seriously. Help please.