Take two children to the back of the hall. One should be year 6 and the other year 1. Place a box of chocolates at the front, and tell them it is treasure. Ask them to race to it, and that the winner gets it. I am assuming that the bigger and stronger child gets to the treasure first (often the children are kind to each other and the bigger lets the younger win, but you need to tell them both beforehand that you do need the bigger and stronger child to win).
She picks it up and says (ask her to repeat after you), 'I got here first. This is mine'.
She gets everything and the smaller child gets nothing.
Ask the other children if that is fair? When they all say, 'No', she then gives to the smaller child one of the sweets, but still keeps the rest for herself.
You could say that is a bit how it is like in our world. The bigger and stronger people get all the world's treasure and, if they are feeling good, they occasionally give one sweet to those who are not so big and strong - but they still keep the rest for themselves.
But then you introduce people to the King.
The King says to the the older child (get the child acting out the role of King to say after you): 'That is not your treasure. I crafted it, left it there, and it is mine'.
Ask the children what the child should do.
Explain that the child could walk away with the sweets and pretend that the King does not exist. She might store them in a safe place, give some to her friends and to the people who do good to her. But when other people ask for some of the treasure, or try to take it, she fights them off. Her problem is that although she pretends that the King does not exist, there will always be something in her which is frightened that the King will come and get her.
Or she can realise that the treasure does belong to the King, say sorry for taking it for herself and offer it back to Him.
If she does that, she gets a surprise. The King says, 'You may keep the treasure. But remember it is not yours. It is my gift, not just to you, but for everyone.'