Hi,

Why class has to be lazy? When I have a class ie:

class A{
private int age;
private string name;
IList children;
}
The first thing is that only collections can take lazy key word and strings, integers etc not and it has sense- collection can be big so we don't want to load it into memory. But the whole above class A even without children parameter has to be lazy - why? Are simple properties also lazy, what for?
And if the whole class is lazy why I have to also mark the collections to be lazy?

You don't have to mark it as lazy

The whole class is a proxy when you reference it as a lazy association,
otherwise - it's not lazy.