Is foot powder a substitute for baby powder on a baby?

PLEASE NO! Babies are so precious that you don't want him to smell bad with foot powder! you can use baby lotion instead.
Generally not. We no longer use "baby powder" made from talc as it can cause lung irritation if the child inhales it during application. Prefer corn starch based powders. Foot powder may have some ingredients in it that could irritation the skin. Avoid excessive powdering - apply with your fingertips to the upper thigh creases. Avoid over the genitals as it can occasionally cause irritation to the urinary exit.