L.A.
There are many public elementary schools that try to hold their school carnivals around that time of year. The kids wear their costumes. Call your local elementary school and see if they are having a carnival. Also some of the churches have non-Halloween carnivals. Hyde Park Baptist Church has a Noahs Ark Carnival around that time. Give their daycare a call.
Many of the Austin Libraries have parties and Halloween storytimes.Also many of the book stores plan events every weekend of October. BookPeople used to have the best childrens activities every Saturday and Sunday. The Austin Childrens Museum has held Haunted houses for young children sometimes at their museum and sometimes at a mall. Just call them. Sometimes the big malls will have trick or treat on Halloween night.