"Alright kiddo, so you know how we have things that we need to be careful about because they could hurt us or others? Those things are called dangerous goods.
Now, imagine that some things are so dangerous that they need to be specially labeled and handled in a certain way so that people can be safe around them. Things like gasoline, explosives, and poisonous chemicals are considered dangerous goods.
When these goods are being shipped or transported, they need to follow very strict rules so that everyone stays safe. The people handling them need to be trained and have special equipment to protect themselves and others.
This is why you might sometimes see big trucks on the road with a sign that says 'hazardous materials.' It's really important that people stay away from them and that everyone takes good care of these dangerous goods. So always listen to your grown-ups when they tell you to stay away from things that could be dangerous!"