If you are using the passcode photos feature (password protecting individual photos in a gallery) and you are doing school photography or something similar where you might have siblings in the same gallery and don't want parents to be able to add photos to the same collection/package, here are some steps to take to stop that.
1) In your collections there is an option "Do not allow adding photos to this collection from different galleries or sub-galleries". You will want to check that when editing your collections.
2) In your gallery, upload all the photos into the main gallery. Then while in the Photos tab of the gallery, select the Create Sub Galleries option. Create a new sub gallery named something like "Siblings".
3) After it is created, check the option that shows above the sub gallery "do not display sub galleries on website".
4) Move the photos of one of the siblings (not both) into that sub-gallery (see below *). You don't have to create a sub gallery for each sibling. You will only be moving one of the siblings into the sub gallery.
* To move existing photos into the sub-gallery
- Check the checkbox under the thumbnails to select them.
- Click into the sub-gallery you created.
- In the menu in the tray at the bottom of the screen select "Add photos to this sub gallery" link.
- In the confirmation menu, select "Add photos to this page and remove from any other pages (move photos)".
Setting it up this way, if the parent adds a collection to their cart then views the other child (which will be in a sub-gallery, but they don't know that), they will not be able to add the other child to that collection.
Also, if you have a required product group, the parent will have to select from the require product group again before adding products from the other product groups to their cart.