No, it doesn't work, and it makes sense too (imo). If `T` is a subclass of `FlxSprite` named `ZSprite` which introduces a new `z`  property, for example, and you make the following call in a `FlxTypedSpriteGroup<ZSprite>`:

`transformChildren(function(s:ZSprite, v:Float) { s.z = v; }, 5.2)`;

How is that supposed to work on a `FlxSprite`, which does not have the `z` property?