People, in general, were often a trigger for Joker's aggressive outbursts. His owners' were very concerned about him around children, in particular.
When I'm working with a dogs, I bring them nearly everywhere I go, including family functions. This allows me to work though real life scenarios.
Last weekend was the perfect opportunity for him to face a situation that would normally have made him uneasy. Look at Joker's body language-- he's relaxed and comfortable in the situation. It was quite natural for him to ease into the situation.
In the video, you can see Joker being a part of the backyard gathering, even while a small child walks by him. Our adolescent Doberman, is actually acting as support for Joker. She understands the behaviour and state of mind that is expected in these situations.
As you know, children can create excitement. There is a moment where Joker becomes curious, and is firmly reminded to go back to submission. By controlling Joker's level of excitement (maintaining a submissive state of mind), he is able to become part of a social setting.