A couple of websites agreed that 1-3yr olds need around 500mg calcium a day - two glasses of milk.
But if they are getting cheese and yoghurt as well as milk - you'll find that they are getting their requirements okay.
Cheers!
This is the standard I go by as well and seems to be pretty universal except in the UK where they say LOs only need 350mg of calcium per day.
A "glass" of milk is 8ounces, so in total LOs need 16 ounces of milk if all of their calcium is to come from milk. Cheese, yogurt, etc are included in the total for dairy.