When my son was younger, this was the time of year that he and I most looked forward to. He would have a costume in mind and I would get to figure out which components we were going to make, and which we need to buy.
Once, I made this clown costume from scratch, having bought the material at Stonemountain & Daughter, but purchased the clown wig and snazaroo face paint at the Halloween Spirit Store (locations below).
Another year, we bought the whole Santa outfit, but I assembled a crafty undershirt strategy that contained a jolly-sized belly. (Hard to see in this photo, so you'll have to believe me.)
Here's where to buy costumes and materials to make them yourself in the East Bay.
Second-hand clothing stores. In October, Goodwill, Salvation Army, and other thrift stores often sell used, but originally store-bought kids' costumes. but they also have the makings for tons of homemade costumes. An old prom dress can become a princess or fairy. If you have low-level sewing skills, it's easier to start with a manufactured garment and leverage the existing hems or zipper closures.
Kids used clothing stores start putting their costumes out during the first week of October. I stopped by Grove Street Kids and they are already ready for you. Check out the following used clothing stores for baby, toddler and preschooler sizes.
Seasonal Costume Stores
Seasonal Halloween Spirit Superstores. These pop-up shops enable landlords to earn some rent while occupying a vacant retail space. This year you'll find a warehouse-style Halloween store, packed with costumes, accessories, and house decorations in these locations already open:
Berkeley, 2450 Shattuck Ave, across from Dollar Tree
Emeryville, 569o Bay Street near Hyatt Place
El Cerrito, 430 El Cerrito Plaza, beside Petco
Pinole, 1500 Fitzgerald Dr, former K-Mart
San Leandro, 1305 Washington Ave near Nation's
Party City (Alameda and Richmond)
I have already extolled the virtues of Party City for Halloween.
For DIY or mostly DIY Costumes
Fabric stores sell patterns for sewers, fabric, yarns and notions. DIYers will find light green furry material for Oscar the Grouch, silver fabric for a knight's cape, or velcro that will be easy to install. Try one of these:
Discount Fabrics (Berkeley at Ashby and San Pablo)
An eclectic assortment of materials, some at great deals.
Jo-Ann's (El Cerrito Plaza and San Leandro)
Make sure to download their app before you go for coupons
Michael's (Emeryville, Alameda, Pinole)
Less fabric, but more poster boards, sticky back felt, and adhesive products.