Is there any way of adding a second iOS app to the account (i.e. Mom).
Are you thinking more of a second login (username/password) than the account holder?
Exactly, so my wife might also be alerted if I miss the notification.
At this time there is not a way to associate different logins, though this is something that would be a great thing to add.
What you want to do is log in with your main account username and password and you will be good to go. Each phone app will be recognized as different phones and be given different names.
We have done this with 3 phones, mine, my husband and my mom. Its great because she is in Northern Cali 9 hrs away and she gets to talk to the kids individually without them fighting over my cell.
Also cool bonus my husband was on a business trip to France and he still got notifications when the kids were trying to reach me and we all got a big surprise when he could talk through the app on the other side of the world!!! We are in Cali