The Thanksgiving Holiday in the U.S. stemmed from the Pilgrims survival of their first harvest in America. The Pilgrims celebrated their success with the Indians in 1621. Officially, Thanksgiving became a celebrated holiday since Abraham Lincoln made it official in 1863.
What we now know as the First Thanksgiving was celebrated by the pilgrims to give thanks for a successful corn harvest. The Native Americans (Indians) joined in celebrating with the pilgrims. At the time, they had no way to know that it would result in a national holiday that is celebrated still.
When the pilgrims celebrated their bountiful harvest, they did not realize that they were starting what was to become a yearly national holiday, but yes, we now consider their celebration the first Thanksgiving.
most likely there were kids in the first thanksgiving. it was celebrated with native americans and pilgrims. also, there was a time when 1/6 th of the Americas were Pilgrims, so there should've been kids to carry the holiday.
As far as the first religious holiday that was celebrated, the most supported holiday is the Jewish Passover. However, the oldest holiday that was celebrated is New Years which is a celebration that begun around 4,000 years ago, celebrated by the ancient Babylonians.