In the song "Frosty the Snowman", what brings Frosty to life?

Frosty the Snowman is a popular song written by Steve "Jack" Rollins and Steve Nelson and was recorded by Gene Autry and the Cass County Boys in 1950. It's considered a Christmas song even though Christmas isn't even mentioned in the lyrics. The lyrics say that Frosty comes to life thanks to a hat: "Frosty the Snowman is a fairy tale, they say. He was made of snow but the children know how he came to life one day. There must have been some magic in that Old silk hat they found. For when they placed it on his head He began to dance around."

Source: Simply Daycare