You'll find lots of Batman ensembles to choose from in stores and online. You can purchase this authentic-looking getup at www.anniescostumes.com, for example.
Or, if a premade costume isn't in your bat budget, opt to make your own. Raid your child's closet for these all-black essentials: shirt, pants, socks, and sneakers or boots. Purchase inexpensive black fabric and transform it into a cape by cutting a scalloped edge along the bottom (make sharp points instead of rounded scallops for a fiercer look).
Add a thick gold belt or sash around the waist and top off the look with an inexpensive Batman mask. And remember: Even though bats usually only come out at night, Halloween is the perfect time for your child to make his daytime debut.