Our version of Mardi Gras, known as "Fastnacht" in Mainz, is known as the 5th season of the year. It begins November 11th and technically ends on Ash Wednesday (see the nice Easter-tie-in), but the big party in Mainz happens the Monday before Ash Wednesday, on "Rose Monday."
That was the background information.
On New Year's Day, the Fastnachters start warming up by putting on a parade. Kids dress up, hence the Return of the Bear.