When my son was 5, I couldn't afford a phone and one Christmas we down the street to make a phone call. The line was busy so we started playing tag and my son turned around and went smack into a high beam and cut hit head wide open.
We didn't have facebook but I didn't call my mother either. I don't recall how she heard about it but it wasn't anything to concern my parents with. I took him to the hospital, he got a few stitches, and I will hang his wrist band on my tree, again, this year.
I will also add that I would not call my mother in law to inform her of any family business. We don't have that type of relationship.
The car and the birthday party ~ I don't know but if you were going through withdraws it could have been for the best. Teenage crowds can be loud and obnoxious. I just think it was rude because it wasn't mentioned when they borrowed your car. I do hope you told her Happy Birthday anyway.
In any case~ I hope your grandchild heals well and you and your son can work on better communication skills since he calls you all the time. unfortunately, I do know that pain. My son now, tells me nothing but we chat. I learn everything through his sister but we're working on it and I'm hoping I'll really connect with his other half but given history, I'm having doubts.