Hifu means a kind of jackets that is put on over kimono. It was favored by the men of taste, such as chajin (master of tea ceremony) and haijin (haiku poet), in the last stage of Edo period, and it later came into use among females. It is the origin of current kimono coat.
Rinzu (Japanese silk satin damask) is generally used as material, and its shape and use are similar to those of haori (Japanese short coat).
Unlike haori, however, its uchiawase (the front panel of cloth of kimono) is wide enough to cover whole the chest, its neckline is banryo (marukubi : round collar) and it's front panels of cloth are tied by braids.
It was originally used by some males for the purpose of cold protection and shielding kimono from dust. However, it's scope of uses became wider gradually, and the term "hifu" normally refers "sodenashi hifu" (hifu without sleeves) for girls if we use this term at kimono shop.
Hifu as haregi (festive dress) for girls
Rinzu of scarlet color is normally used as material. Unlike hifu for adults, it has no sleeves and an ornament of chrysanthemum knot made of a silk string is often attached on the shoulder sections of uchiawase.
It is used mainly by girls under the age of 10 probably for the purpose of protecting kimono from tainting and is seldom used by boys or older girls.
When we order a set of clothes for shichi-go-san at a dress rental firm, hifu is usually included in the set.