Q: can i facetime my son on devices with the same apple id

No,  you would need a separate Apple ID set up for Facetime on one of the devices to Facetime with it.

Settings->Facetime->Apple ID

You can change the Facetime ID only and leave everything else still associated with the other ID for content access, and icloud sync.

I am going to disagree with my esteemed colleague on this because you need only assign a separate email address on his iPad as the contact address for FaceTime. It does not have to be an Apple ID. I did this for months until all of my family members got our own iPhones and now we use the iPhone numbers as our contact at address.

This video explains how to do it.

http://macmost.com/setting-up-multiple-ios-devices-for-messages-and-facetime.htm l

I tried that before, and it would not work. Assigning a different Address in the "You Can be Reached By Facetime At" section assigned the address to all the devices under the Apple ID there. So when attempting to call that address, the call would fail. Removing the address on one device, would remove it from all the devices.

I was only able to call my iPad from my iPhone when  I changed the Apple ID for Facetime to a different one.

But I will not discredit your experience Demo.  There's no harm in trying it out anyway.

I'll have to second Demo on that. It certainly can be done with a single AppleID and different send/Receive for FaceTime. Just did it, in fact.

Have him use an email address like gmail.com. If both devices are using the same address, it's like calling your own phone.

Unable to make or receive FaceTime calls after April 16, 2014

http://support.apple.com/kb/TS5419

Using FaceTime http://support.apple.com/kb/ht4319

Troubleshooting FaceTime http://support.apple.com/kb/TS3367

The Complete Guide to FaceTime + iMessage: Setup, Use, and Troubleshooting

http://tinyurl.com/a7odey8

Troubleshooting FaceTime and iMessage activation

http://support.apple.com/kb/TS4268

iOS: FaceTime is 'Unable to verify email because it is in use'

http://support.apple.com/kb/TS3510

Using FaceTime and iMessage behind a firewall

http://support.apple.com/kb/HT4245

iOS: About Messages

http://support.apple.com/kb/HT3529

Set up iMessage

http://www.apple.com/ca/ios/messages/

iOS and OS X: Link your phone number and Apple ID for use with FaceTime and iMessage

http://support.apple.com/kb/HT5538

How to Set Up & Use iMessage on iPhone, iPad, & iPod touch with iOS

http://osxdaily.com/2011/10/18/set-up-imessage-on-iphone-ipad-ipod-touch-with-io s-5/

Set Up Alert Sounds

http://www.quepublishing.com/articles/article.aspx?p=1873027&seqNum=3

Extra FaceTime IDs

http://tinyurl.com/k683gr4

Troubleshooting Messages

http://support.apple.com/kb/TS2755

Troubleshooting iMessage Issues: Some Useful Tips You Should Try

http://www.igeeksblog.com/troubleshooting-imessage-issues/

Setting Up Multiple iOS Devices for iMessage and Facetime

http://macmost.com/setting-up-multiple-ios-devices-for-messages-and-facetime.htm l

FaceTime and iMessage not accepting Apple ID password

http://www.ilounge.com/index.php/articles/comments/facetime-and-imessage-not-acc epting-apple-id-password/

Fix Can’t Sign Into FaceTime or iMessage iOS 7

http://ipadtutr.com/fix-login-facetime-imessage-ios-7/

FaceTime, Game Center, Messages: Troubleshooting sign in issues

http://support.apple.com/kb/TS3970

Unable to use FaceTime and iMessage with my apple ID

https://discussions.apple.com/thread/4649373?tstart=90

iOS 7 allows you to block phone numbers or e-mail addresses from contacting you via the Phone, FaceTime, or Messages

http://howto.cnet.com/8301-11310_39-57602643-285/you-can-block-people-from-conta cting-you-on-ios-7/

How to Block Someone on FaceTime

http://www.ehow.com/how_10033185_block-someone-facetime.html

My Facetime Doesn't Ring

https://discussions.apple.com/message/19087457#19087457

How to watch FaceTime calls on the big screen with Apple TV

http://www.imore.com/daily-tip-ios-5-airplay-mirroring-facetime

Send an iMessage as a Text Message Instead with a Quick Tap & Hold

http://osxdaily.com/2012/11/18/send-imessage-as-text-message/

To send messages to non-Apple devices, check out the TextFree app https://itunes.apple.com/us/app/text-free-textfree-sms-real/id399355755?mt=8

How to Text on the iPad

http://ipad.about.com/od/ipad_tricks/a/How-To-Text-On-The-Ipad.htm

How to Send SMS from iPad

http://www.iskysoft.com/apple-ipad/send-sms-from-ipad.html

How to Receive SMS Messages on an iPad

http://yourbusiness.azcentral.com/receive-sms-messages-ipad-16776.html

Apps for Texting http://appadvice.com/appguides/show/apps-for-texting

You can check the status of the FaceTime/iMessage servers at this link.

http://www.apple.com/support/systemstatus/

 Cheers, Tom

I suggested this, because like I said, we did this for months before we all got iPhones. I know that it works.