Are there filters, firewalls, or blocks put on the devices prior to distribution or is the full internet available?
In order to understand filters, firewalls, and blocks, we have to discuss this on the school system's network and off the network.
When the devices are connected to the school networks using WiFi, they are considered secure devices. Filters are in place to keep students away from inappropriate and non-educational internet sites and the school system's firewall helps protect other users from "hacking into" each other's devices. Our district internet filter currently blocks the categories that have been deemed inappropriate and/or that violate CIPA (Children’s Internet Protection Act). The filter list also includes a customized feature that is updated anytime a site is found to be inappropriate or not needed at the school level.
When at home or using a public WiFi spot, the devices are only as secure as the network being used. Filters would most likely not be in place so it will be up to the parents to monitor usage. Firewalls are not in place from a network standpoint although most agree that Apple devices are more secure than Windows-based devices. However, there have been instances of Apple devices being accessed by others on public WiFi if passwords are weak or not being used. Sensitive information should not be shared over these networks for anyone on any device.
Will it be permissible for parents/families to download additional internet safety/protection on the device?
Yes, just be aware that some of these applications might prevent an app from working properly or restrict access that might be needed for instruction.
Parents can enable Restrictions, also known as parental controls, on iPhone, iPad, and iPod touch. Restrictions stop you from using specific features and applications. Parental controls are not available on the MacBook Airs because the user accounts are locked at the district level.
Here is a sheet that tells you how to set up restrictions on the iPad. Below is a video to show you how to set up restrictions on the iPad. Please note: If the passcode prevents a student from doing particular work on the iPad, they may have to complete an alternate assignment. Also, if you lose the restrictions passcode, we would have to reset the iPad to factory settings in order to clear the passcode. This means that all work on the iPad could be lost. 
