Got this from: http://www.bev.net/education/SeaWorld/baleen_whales/birthbw.html

--The calf suckles from nipples concealed in its mother's abdominal mammary
slits. Calves nurse under water, close to the surface.
--A high fat content (up to 40% to 50% fat) allows the calf to rapidly
develop a thick insulating layer of blubber.
--The nursing period lasts from 4 to 11 months. A calf is weaned by its
first summer in time to feed.

As for that last item, in looking for this info I read that whales/dolphins
nurse up to 3 years depending on dyad. Now I'd wonder if this info relates
only to captive animals. More info:
Sei whales are 4.5 m (15 ft.) at birth and grow about 2.5 cm (1 in.) each day.

--Blue whale calves gain 90 kg (200 lb.) each day while nursing.
--Gray whale calves double their weight in about three months and double
their length in about two years.
--Humpback whales grow 45 cm (1.5 ft.) per month during nursing.
--ccording to research in zoological parks, the composition of beluga milk
varies widely among individuals and fluctuates throughout the nursing
period. Beluga milk may average 28% milkfat, 11% protein, 60.25% water, and
less than 1% ash (SWT). The milk contains approximately 92 calories per ounce.
--Beluga calves are dependent upon nursing for the first year, until their
teeth emerge (Katona, Rough, and Richardson, 1983). They then supplement
their diets with shrimps and small fishes (Haley, 1978). Most calves may
nurse for 20 to 24 months (Nowak, 1991). Some have been documented to nurse
as long as two years (Katona, Rough, and Richardson, 1983).

I know I've seen photos before, but I just can't find them. The teat is
similar to an elephants--very long and skinny (sort of like a sausage).

--Kelly