public class ParentEntity
{
    private readonly Action<object, string> _lazyLoader;

    public Guid Id { get; set; }
    public string Name { get; set; }

    private List<ChildEntity> _children;
    public List<ChildEntity> Children
    {
        get
        {
            if (_children == null)
            {
                Console.WriteLine($"WARNING: Lazy Loading {nameof(Children)}");
                _lazyLoader?.Load(this, ref _children);;
            }

            return _children;
        }
        set => _children = value;
    }

    public ParentEntity(Action<object, string> lazyLoader)
    {
        _lazyLoader = lazyLoader;
    }

}

public class ChildEntity
{
    public Guid Id { get; set; }
    public Guid ParentId { get; set; }
    public string Name { get; set; }
}

public static class PocoLoadingExtensions
{
    public static TRelated Load<TRelated>(
        this Action<object, string> loader,
        object entity,
        ref TRelated navigationField,
        [CallerMemberName] string navigationName = null)
        where TRelated : class
    {
        loader?.Invoke(entity, navigationName);

        return navigationField;
    }
}