My ex wife does not tell me if my kids are in hospital - I just dont understand it?

It has happened three times now.  The first 2 times I let it go, but this time I am just plain angry about it.  My 13 year old is in hospital (Emergency section) with blood infections has numerous drips etc etc - and is quite sick.  Not life threatening, but still very upsetting to me and certainly to him.  He is over 8 hours away.  When I found out from one of my other kids (3 of which live with her) I was so angry, I could not talk to her.  I called dozens of hospitals to find out which one he was in, and after finding him, could not get any information, as she had listed herself as the sole contact.  After discussing it with the nurse, and after her discussing it with my sick child, all is OK, I can now call and ask about him.  I see my kids every couple of weeks, and speak to them every couple of days.

This could be a long question, with all sorts of comebacks, but in short I am a good person, am very close to my kids, and they are very close to me.  I have never said bad stuff about her and have no history of violence.  In other words, my question is simple.

Why would my ex wife think it is OK to not let me know about one of my kids in hospital?  She has moved on with her relationships, as have I, we divorced some 6 years ago.  I would have thought that even if I was in jail for serious crimes, that I would have the right to know (and she would have the responsibility to tell me either directly or indirectly via a 3rd party) that one of my kids is quite sick.

I am sure there is a logical reason, but after 24 hours I just cant see it, and I am more angry now with her than I have ever been in my life.  I am not the sort that would do something stupid, but I just dont get it.