The 助動詞（じょどうし） (auxiliary verbs) せる and させる will be modified in 関西弁（かんさいべん）, creating a new form that interacts with the 未然形（みぜんけい） (indeterminate form) of verbs. In the case of う - Verbs, this is the form that interacts with ない, not the form that interacts with う. In standard Japanese, the せる and させる forms are referred to as ‘causative’ (someone/thing is made to perform an action). This meaning stays the same in the Kansai dialect.
The kansai form of せる will be す (with う - Verbs), while させる will become さす (with る - Verbs, する, and くる).
I make the baby eat baby food.
If you make my son go shopping alone, he spends money frivolously.
When I get tired, I make my wife drive.
You're going to make them pick us up? Isn't it faster to walk home?
Caution - These short forms of せる and させる are ‘preferred’ in the Kansai dialect, but are not a requirement. The standard forms may still occasionally be heard.