This is a great way to take kids to a concert. The price is right, FREE! You can bring your own refreshments (especially nice when it's going to be 100+ degrees). You can make yourself (and your kids) comfortable (bring lawn chairs and/or a blanket). There is a playground nearby to entertain the kids while you wait (you will probably want to get there a little early to stake out a spot).
If I remember correctly from last year, they usually have a few vendors selling food (I think I remember tri-tip sandwiches and the A&W truck selling rootbeer and rootbeer floats). If you don't want to bring your own refreshments, I bet you can find something there.
To get to the City Park take Hwy 65 through Exeter. Turn left on Chestnut. The park is located between D and E Streets. It's only about 20 mintues from Porterville. Parking is free. Another bonus, you can get gas at the Arco in Lindsay (right off Hwy 65 by Burger King), yesterday it was $3.69--way cheaper than any place in Porterville!