Introducing Cow's Milk

[Tiana]

When and how did you introduce cow (or other) milk into your child's diet?

My son is almost 2.5 and still nurses at least 4 times a day.  He has a bit of milk on cereal from time to time, but is not really drinking cow's milk yet.  He's never been the best eater, and I've been a bit concerned about him filling up too much on cow's milk, so I haven't really given him it yet.  The older he gets, though, the harder I'm finding it to start him on it.  

How important is it that he be drinking cow's milk?  Should I start giving him glasses of it?  For what it's worth, he loves yoghurt and usually eats it everyday.