Made out of sack clothing filled with straw for bulk, which Son of Mine used as inanimate materials to put into humanoid shapes, scarecrows were given simple life; this included rather basic motor and sensory abilities through the process of molecular fringe animation. They also had "eyes" that came with limited vision. Shoes provided their straw-filled legs with a strong base.
Feeling no pain, these scarecrows marched without an end when advancing on enemies. They were susceptible to bullets, which made them fall to the ground as if dead. Son of Mine would say "reanimate" and all scarecrows would get back up without issue. Additionally, any scarecrow that so much as lost humanoid form could not mend itself. (TV: The Family of Blood)
The scarecrows were used as an army to attack Farringham School for Boys, where many were shot down. Eventually, they re-animated to do more of the Family's bidding. They were made inanimate again after the Family's defeat, as they had no orders left to take. Son of Mine was dressed up as a scarecrow, suspended in time, and left permanently immobile but aware of his fate, and compelled by the Tenth Doctor to guard an English field forever. (TV: Human Nature/The Family of Blood)