The Australian-English phrase happy little Vegemite denotes a contented person—also, in early use, a child.

This phrase originated in advertisements for Vegemite, a type of savoury spread made from yeast extract and vegetable extract.

The proprietary name Vegemite is apparently from:
– vege-, in vegetable;
– -mite, in Marmite, a proprietary name for a type of savoury paste made from yeast extract and vegetable extract.

The following is from Trade Mark Applications: Officially Accepted List, published in the Daily Commercial News and Shipping List (Sydney, New South Wales) of Thursday 27^th December 1923:

List of Commonwealth Trade Mark Applications officially accepted and advertised—November 9, 1923:—
[…]
Vegetable extracts for use as food or as ingredients in food. Word “Vegemite”—Fred. Walker & Co. Pty., Ltd., Melbourne.

The earliest advertisements for Vegemite that I have found used happy little Vege-mite, with wordplay on the noun mite, denoting a small child—as, for example, in the following from The Northern Star (Lismore, New South Wales) of Monday 21^st September 1953:

ARCHER AT 5!

No Cow boys and Indians for Rex Racklyeft—he’s a real archer—a member of Sydney’s St. George Archery Club, at 5!
“Rex has the makings of a champion,” says his father, Club Official. “Tons of energy—Vegemite helps keep him healthy and active”. He’s another happy little “Vege-mite”!
Vegemite provides a rich supply of Vitamin B1, B2 and Niacin. You need these Vitamins every day for healthy nerves, firm body tissues, good digestion. Vegemite is so rich in these essential vitamins because it’s a pure yeast extract. Put Vegemite next to the pepper and salt whenever you set the table. Vegemite—made by Kraft.

In the 1950s, radio advertisements for Vegemite used Happy Little Vegemites, a jingle set to a marching tune. It was later adopted as the soundtrack to television advertisements.

In Happy Little Vegemites (1959), published in Australian Screen, Maryanne Doyle explained:

There were a number of versions of the ‘Happy little Vegemites’ jingle recorded in the 1950s. […] The most famous version [was] recorded in the EMI Studios in Sydney in the late 1950s. It includes singer Betty Parker, dubbed the queen of commercials, imitating a child’s voice, as well as her younger siblings Julia and Stephen Parker, who were children at the time. The solo voice at the end of the song belongs to Betty’s daughter, Linda Marcy.
Alan Weekes, a jingle writer for advertising company J Walter Thompson in Sydney, composed the tune but it was Bob Gibson, a famous band leader and musical director, who set the style by arranging it as a 6/8 march. The marching arrangement of the tune of Happy Little Vegemites has been used in advertising campaigns for Vegemite ever since.

These are the lyrics of Happy Little Vegemites:

We’re happy little Vegemites as bright as bright can be,
We all enjoy our Vegemite for breakfast, lunch and tea,
Our mummy says we’re growing stronger every single week,
Because we love our Vegemite,
We all adore our Vegemite,
It puts a rose in every cheek!

These are, in chronological order, the earliest occurrences of the phrase happy little Vegemite that I have found:

1-: From a letter published in The Sun-Herald (Sydney, New South Wales) of Sunday 3^rd August 1980—with reference to television advertisements:

I’m curious about what types of people in the advertising game are responsible for the ideas behind the commercials which interrupt our viewing so frequently.
More thought should be put into their production. For instance, there’s the ad for a new shoe-cleaner which enables junior to clean his own shoes—on the dining room table! Not at our house, thank you.
Then there are those happy little Vegemites who storm the table and grab—no “please” or “may I?” The beautiful Mum who is contentedly making sandwiches doesn’t practise much hygiene as she licks away at her fingers then goes back to making sandwiches.
Mrs M. J. STRANSKY,
Port Kembla.

2-: From The Bulletin (Sydney, New South Wales) of Tuesday 14^th April 1981:

Mighty hike on Vegemite
Expatriate Australians living in Italy have to pay dearly to be “happy little Vegemites.” An advertisement in Italia-Australia Life!, a bilingual cultural magazine circulating in Italy, offers 230-gram jars at the “special” price of 4000 lire, or about $4.20, for those who care to fill in the order form.
At that price, it is more likely to put a hole in the pocket than a “rose on every cheek.”

3-: From A stitch in mine saves nine, by Mike Gibson, published in The Australian Women’s Weekly (Sydney, New South Wales) of Wednesday 6^th May 1981:

We’ve got five kids. We figured we’d done our bit to help populate Australia, churned out our share of happy little Vegemites.

4-: From the classifieds, published in The Canberra Times (Canberra, Australian Capital Territory) of Friday 1^st April 1983:

21^st BIRTHDAY

HAPPY 21^st to the bloke who keeps the A.C.T.E.A in business.
HAPPY 21^st to the Vegemite Kid.
KIRBY.—Happy Birthday Darling. Love Mum, Dad and Budge.
KIRBY.—Happy Birthday Sis. Love Jackie.
KIRBY Yvonne.—Love and best wishes always, Mick, Dianne, Julie and Angie.
KIRBY.—Happy Birthday Yvonne. Love Alan.
TO the happy little Vegemite— 21^st Birthday Wishes. Love from all your Wizzies.