The "Preserve Child Size" option preserves a target from being rescaled when you rescale the parent Image Target;
for example, if you have an Image Target associated with a Device Database (so the Dataset XML specifies a given size for the target),
and you have a 3d object with a given size attached under your target, this is what happens normally:
- Preserve Child Size is OFF (disabled): if you change the XML size and apply the changes to your Image target, its child 3D object will also be scaled proprotionally, so that it maintains the same relative proportions with the parent target
- Preserve Child Size is ON (enabled): if you change the XML size and apply the changes to your Image target, its child 3D object will NOT be re-scaled, i.e. it will maintain its current size (and so it will NOT maintain the relative proportion with the parent size)
This makes sense for Image Targets which are associated to Device Databases, because in that case the size of the target is known a-priori and is simply coming from the XML size settings of your dataset.
However, for Cloud targets, the actual size of the actual target would not be known in advance, because this will only become available at runtime when a Cloud target is recognized (and the target gets instantiated out of it). Therefore, the preseve child size has no effect for Cloud targets (i.e. in the Editor the child augmentation always rescale with the parent).
Note that you can alwyas rescale your target programmatically with a script, so that the absolute size of your target is maintained to the desired value; this can be done at application logic, with some calculations based on the size of the recognized Cloud target.