Okay kiddo, imagine you and your friend like to trade toys. You trade your teddy bear for your friend's toy car. But what if your friend doesn't give you a fair trade? What if they take your teddy bear but don't give you their toy car? That wouldn't be fair, would it?
Now imagine that instead of trading toys, countries trade things like food and clothes. Sometimes, rich countries take advantage of poor countries and don't give them a fair trade. They might pay very little for the food or clothes they buy from the poor country, but then charge a lot of money when they sell those things in their own country.
This is where the trade justice movement comes in. It's a group of people who think that all countries should be treated fairly when they trade with each other. They want rich countries to pay fair prices for the things they buy from poor countries, and to make sure that the people who produce those things are treated well and paid fairly.
They also want to make sure that the environment is protected when things are traded. Sometimes, when companies make things to sell, they harm the environment by using too much energy or by polluting the air or water. The trade justice movement wants to make sure that companies are responsible and don't harm the environment.
So, just like you and your friend want to make sure you trade toys fairly, the trade justice movement wants to make sure that countries trade fairly with each other and that everyone involved is treated well.