Apple has their own rating system. Whether you read this and pay attention to it is between you and your youngster.
ESRB doesn't have a place, and most likely never will, on the App store
^This.
Next time you open up Diner Dash look on the bottom right hand side. It should say Rating 4+
It would be a nice thing for ESRB to enter the App Store, nevertheless Apple seems to have its own rating since you can filter in the Parental Controls on the iPhone.