I’m a windshield wiper
(bend arm at elbow with fingers pointing up)
This is how I go
(move arm left and right, pivoting at elbow)
Back and forth, back and forth
(continue back and forth motion)
In the rain and snow.
(continue back and forth motion)

(I've also seen this as a bounce for babies.)

Source: http://www.colapublib.org/children/storytime/toddlerguides/transportation.pdf