Martin Luther King Day

This is a bit late, but
Happy Martin Luther King Day
I tried to bring this up with the kids today, but they didn't really understand what I was on about. I couln't really find any appropriate material and I'm pretty useless myself on this sort of thing. We listened to a bit of the speech about:
'I have a dream that one day little black boys and black girls will be able to join hands with little white boys and white girls as sisters and brothers...'
while looking at some websites