Holly went onto cows milk at just after 12mths, but only because I am ocd about sugar and read how much there is in follow on milk
She STILL wont drink it cold, has to be zapped in the microwave for 20 secs to take the chill off.
Remember that any yogurt, cheese, green veg, some pulses, fish, bread - loads of stuff has calcium in in too.
Holly usually only has 9oz of milk max per day - but she has other calciummy foods.
If you are worried about nutrients, there are loads of great baby/toddler vitamins out there. We use abidec multivit and omega 3 (recommended by paediatrician).