The Managed Delivery job would be created on the parent NS, and filter down to the children NS and then to the clients off of all.
For the download of the package, the software resource will be created on the parent NS, and the package will replicate out to the site servers on it, and off the children NS.
The package source will be the parent NS for the site servers on the parent, and then the site servers for the children NS will be based on the site configuration on the parent.
Requests for the package, from clients off the children NS, will be forwarded up to the parent NS.