Q: how can I activate my Iphone 3s if it´s blocked

If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support

Hi mialmacenmystore,

I understand your son was using your iPhone then got it blocked and you're now receiving a message on the iPhone saying that it's deactivated and it needs to be connected to iTunes. Because you said the phone is giving you a message saying the iPhone is deactivated, and if you can't activate it, then I think this knowledgebase support article from Apple should help you: If you can't activate your iPhone - Apple Support.

Otherwise, if you're locked out, then the guide suggested by the user previously above me should help you.

I hope this helps you.