I wouldnt give them any milk to take unless they asked for it - in which case give them the one you know they will drink otherwise it will end up thrown out no matter how good it is for them!
Cow milk is a great food for calves, they thrive on it. Why give it to to human children though? Why choose this particular animal to drink its mamalian fluid? What would you think if you were offered, say, pig milk, or dog milk? Like countless millions you have been led to believe that this is somehow healthy nourishment for your child. I suggest you give him/her fruit juice.