Richard Gray, 36, admitted intending to cause fear of violence with the fake firearm near Heene and St Mary's Primary Schools on 8 May.
He also admitted possessing a knife in Worthing's Victoria Park.
Gray, of Cortis Avenue, was sentenced at Crawley Magistrates' Court to eight weeks in prison for each offence, to run concurrently.
A man has been jailed for trying to scare people with an imitation gun near two Worthing schools.