Use an important scientific technique to solve the mystery of who stole the chocolate!
I’d recommend watching the video then setting up your own chocolate mystery for your children to solve. Test it first with two different brands of black felt-tip pen to check the colour splitting is different enough to be told apart. We used Berol and Crayola.
Let the children play with different colour pens for a while first to familiarise themselves with the concept of chromatography.