In our house we take time on important days to explain to our children why we are observing something important on that day. Martin Luther King, jr made some praiseworthy contributions to the history of our country and is worth remembering on the day our country has set aside to honor him. He is also an excellent example of a godly man who gave his live for the cause of freedom.
When I'm teaching my children about something important I always like to use books and last year I blogged on my favorite book for children in early elementary, My Brother Martin. My children also viewed a video "Our Friend Martin" about two boys who go back in time to meet Martin Luther King, jr.
Please let me know in the comments if you have found other good resources. Whatever you do on this day take time to remember this great man and to say thanks to God for people like him willing to speak out for all God's people.