Data on the average volume of milk consumed by nursing children (for Ana
Rita Guzmn, Jon Mirsalis, and interested lactnetters) is amazingly hard to
come by!  You can tease it out of these studies, which generally have tiny
sample sizes.  If anybody knows of other research, I'd be very interested
to know the references; I've scoured the literature and I really think
this is all we have to go on at the present time:

Allen-J-C.  Keller-R-P.  Archer-P.  Neville-M-C.  Studies in human
lactation: milk composition and daily secretion rates of macronutrients in
the first year of lactation.  AMERICAN JOURNAL OF CLINICAL NUTRITION 1991
Jul.  54(1).  P 69-80.

Arthur-P-G.  Smith-M.  Hartmann-P-E.  Milk lactose, citrate, and glucose
as markers of lactogenesis in normal and diabetic women.  JOURNAL OF
PEDIATRIC GASTROENTEROLOGY AND NUTRITION 1989 Nov.  9(4).  P 488-96.
In this study, the average milk intake is reported:
24 hours after birth    = 82 cc/day
6 days after birth      = 18.5 oz/day

Casey-C-E.  Neifert-M-R.  Seacat-J-M.  Neville-M-C.  Nutrient intake by
breast-fed infants during the first five days after birth.  AMERICAN
JOURNAL OF DISEASES OF CHILDREN 1986 Sep.  140(9).  P 933-6.
The intakes of milk during the first 120 hours after birth were measured
in 11 full-term, breast-fed infants.  Data is reported as g/kg/day, and I
figured that, for a baby weighing 3.5 kg, intake would be:
first 24 hours  = 45 cc (range, 10.5 to 112 cc)
day 3           = 11 oz (range, 6 to 19 oz)
day 5           = 18 oz (range, 13 to 23 oz)

Neville-M-C.  Allen-J-C.  Archer-P-C.  Casey-C-E.  Seacat-J. Keller-R-P.
Lutes-V.  Rasbach-J.  Neifert-M.  Studies in human lactation: milk volume
and nutrient composition during weaning and lactogenesis.  AMERICAN
JOURNAL OF CLINICAL NUTRITION 1991 Jul.  54(1).  P 81- 92.

Neville-M-C.  Keller-R.  Seacat-J.  Lutes-V.  Neifert-M.  Casey-C.
Allen-J.  Archer-P.  Studies in human lactation: milk volumes in lactating
women during the onset of lactation and full lactation.  AMERICAN JOURNAL
OF CLINICAL NUTRITION 1988 Dec.  48(6).  P 1375-86.
Milk yield (measured in 13 multiparous exclusively breastfeeding Caucasian
women) was low on days 1 and 2, increased rapidly to 498 +/- 129 grams/day
on day 5, and then more slowly to 753 +/- 89 g/d during months 3-5.

Saint-L.  Maggiore-P.  Hartmann-P-E.  Yield and nutrient content of milk
in eight women breastfeeding twins and one woman breastfeeding triplets.
British Journal of Nutrition.  1986.  56(1).  pp 49-58
At 6 months, mothers fully breastfeeding twins had average milk yield of
67 oz/day.  The mother of triplets had average milk yield of 103 oz/day.

Saint-L.  Smith-M.  Hartmann-P-E.  The yield and nutrient content of
colostrum and milk of women from giving birth to 1 month post-partum.
BRITISH JOURNAL OF NUTRITION 1984 Jul.  52(1).  P 87-95.
Milk intake of from delivery to day 5 post-partum was determined by
test-weighing nine infants using an integrating electronic balance. The
mean yield was:
first 24 h after birth  = 37 (range 7.0-122.5) g/24 hours
day 3                   = 408 (range 98.3-775) g/24 hours
day 5                   = 705.4 (range 452.5-876) g/24 hours
day 14 to 28            = 1.156 (SD 0.167) kg/24 hours

Hope this helps!

Ginna Wall, MN, IBCLC, Lactation Services Coordinator
University of Washington Medical Center, Mailbox 356153
1959 NE Pacific Street, Seattle WA 98195
Voicemail: (206)548-6368, Fax: (206)548-7665