void CreateAllChilds()
{
List <ChildViewModel> all =
(from child in _childRepository.GetChilds()
select new ChildViewModel(child, _childRepository)).ToList();
foreach (ChildViewModel cvm in all)
{
cvm.PropertyChanged += this.OnChildViewModelPropertyChanged;
}
this.AllChilds = new ObservableCollection <ChildViewModel>(all);
this.AllChilds.CollectionChanged += this.OnCollectionChanged;
}