The major food component in ice cream is milk and, of this, milk protein is the most important. There is more milk protein in a quality dairy ice cream than in the same weight of milk. In addition, milk contains calcium and phosphorus which are very important in the building of bone, along with some essential vitamins.
Fat is necessary in a balanced diet to provide energy, along with sugars including lactose from the milk. Milk fat is especially useful in that it will normally contain Vitamins A and D. It is only when fat and sugar are taken in excess that they can lead to overweight, particularly if little or no exercise is taken.
Another important aspect is that ice cream is very easily taken by sick people and particularly children. Its soothing feel is very helpful if you have a cold or throat infection. For those people who are unable to have ordinary sugar (diabetics for example) there are ices specially formulated for them which are extremely palatable and can give a very useful addition to their limited diet, while very similar ices are available for those who have to 'watch the inches'