If Good Friday is the day on which Jesus Christ was crucified, why is it called good? Here is the best explanation I’ve seen on the internet:
http://christiancadre.blogspot.com/2007/04/why-is-it-called-good-friday.html
Kidzworld has a page for kids about Good Friday, complete with activity ideas:
http://www.kidzworld.com/article/4354-good-friday
The Free Resource shares some interesting facts about Good Friday:
http://www.thefreeresource.com/facts-about-good-friday-for-kids
Cornerstones for Parents offers some tips for talking to young kids about Good Friday:
http://www.cornerstonesforparents.com/talking-young-kids-good-friday-easter
And finally, Wikipedia has a description of the Biblical account with links to corresponding scriptures at BibleGateway.com: