I dont mean to be argumentative Rosehip Fairy, but dairy is actually a very poor source of calcium. Although it contains high amounts it is in a form which is not easily utilised by the body. In fact it can even leach calcium form the bones in some cases, which is why we see such a large amount of osteoporosis in western societies where a lot of dairy is consumed, yet very little in countries such as Japan where dairy products are rare.
You are right that babies and children need calcium for strong bones though, as well as many other biological mechanisms as calcium is an electrolyte which is essential to every cell in the body. The best sources of calcium are fish, beans, peas, green leafy vegetables, nuts, and oranges, to name a few.