Looking into these websites, you will understand what slavery meant and how it did affect Africa and African people. You will understand why it was so important for the European economy and try to find the dates of abolition. At last, try to discover the links between slavery and the United-States and how this « trade » helped to build America.
Useful websites
Website for (British) children
Site of a museum, look at the slave's stories
http://www.liverpoolmuseums.org.uk/ism/
The story of a Danish slave ship
http://www.unesco.no/fredensborg/index.htm
Another docuymentrary on a wrecked ship (lots of photos)
http://ngm.nationalgeographic.com/ngm/0208/feature4/index.html
BBC (clear, simple but not for children so don't worry if you don't understand!)
http://www.bbc.co.uk/abolition/
Site of Bristol, a slave port like Nantes or Bordeaux in France
http://www.discoveringbristol.org.uk/
Very interesting site but quite difficult
http://www.antislavery.org/breakingthesilence/