MongoDb : How to insert additional object into object collection?

As other mentioned, The structure you want is not valid. I recommend the following structure for your owner document:

    {
    "_id" : ObjectId("51c9cf2b206dfb73d666ae07"),
    "firstName" : "john",
    "lastName" : "smith",
    "ownerEmail" : "[email protected]",
    "camps" : [
            {
                    "name" : "cubs-killeen",
                    "location" : "killeen"
            },
            {
                    "name" : "cubs-temple",
                    "location" : "temple"
            }
    ],
    "instructors" : [
            {
                    "firstName" : "joe",
                    "lastName" : "black"
            },
            {
                    "firstName" : "will",
                    "lastName" : "smith"
            }
    ]
}

and then

db.stack.update(
  { ownerEmail: "[email protected]" },
  {
    $push: {
      camps: { name: "cubs-killeen", location: "some other Place" }
    }
  }
);

Having this, you can add camps like this:

Hope it helps.