Greensleeves is almost 500 years old. I'm sure there were other very popular songs when it came out, but Greensleeves had to staying power to still be here. What do you think is today's Greensleeves?
Not sure about today's, but I think the one from the 18th century is Ah! vous dirai-je, maman, better known in English as Twinkle Twinkle Little Star or the alphabet song.