Note: Asset Types is a professional/enterprise license feature
With Asset Types configured it is possible to download child assets directly from their parent asset pages. This makes it quicker to download assets that are often required as a pair (eg. a photograph and it's model release form).
To enable this feature go to Admin > Asset Types and click 'Edit' next to your chosen parent asset.
Towards the bottom of the page is the option 'Can download children from parent page?' which will need to be ticked.
Once you've saved go to an asset of the parent asset type you changed and if any children assets are assigned you will see the option to download them.