What model Linksys router? I can't say much about the older ones, but my EA2700 (less than a year old) I can do MAC filtering, and apply parental controls, such that I can limit what a specific device, by it's MAC address can get to... However you need to know what the MAC address of the device is to make this work (If your network is small enough, it is pretty easy to figure out what device has what MAC address). Let me know, if it is similar to the EA2700 I can shoot you the info on how its done...
Perhaps someone more familiar with Apple iOS will chime in here and let you know if there is some sort of filtering / parental control app for your device.