I have bad memories of days spent slaving over some darling little thing only to be loudly rejected by a fickle toddler who declares ten minutes before trick or treating that he doesn't WANT to be a lion anymore.
A few years later I remember walking through the streets with a knight in shinning armor who was anything BUT chivalrous: he wanted the same Ninja costume all his friends were wearing.
My kids and I have reached a compromise of sorts: either they pay for store-bought costumes out of their allowance (including tax and shipping -- which means they have to save for about 3 months for the average Ricky outfit with plastic accessories), or they have to graciously accept my free services, submit to fittings, and swear an oath not to change their minds at the last minute.
For my part I have abandoned the labor intensive full body outfits. Regular clothes with a few choice accessories can have just as stunning an effect. I don't want to spend more than a day on a costume.
These are not instructions on making any single costume, rather tips and photos which are designed to help you imagine and craft your own.
Step 1: Comfort
Where I live Halloween is a particularly difficult time of year to design for, because it can be crisp and beautiful, or freezing. Layers which are part of the design (such as a cape, or removable gloves and hat) are the best way to deal with the weather.
Allowing for body movement is very important, especially for determined trick or treaters. Any accessory must leave at least one hand free. If you saddle your young cowboy with a hobby horse you will end up carrying it around the whole time. Take all the pictures you want before you set off, then leave the cumbersome accessories at home.
To avoid loud complaining or an outright refusal to set feet into your creation, any cardboard based costume should no go lower than the hips. For a long skinny costume, such as the classic giant pencil, try making the lower part out of fabric (if it's attached at the bottom to a small hoop it will keep a well defined circular shape). Not only would it be easier to walk in, but the kid would be able to sit down and rest once in a while.