Elizabeth Garcia, 19, was arrested Friday and charged with the attempted murder of her 2-month-old.
The Monroe County Sheriff's Office said a video, sent to investigators with the Department of Children and Families, shows Garcia trying to hit the child with a piece of concrete.
WPLG-TV was told that when Garcie tried to strike the child, two men nearby were able to stop her.
The attack allegedly happened on Aug. 18. Deputies said they were called to Garcia's home in Marathon that same day. She allegedly pulled out a knife in a confrontation with deputies and was charged with carrying a concealed weapon.
Authorities said no one at the time mentioned the incident with the child.