This question seems a little bit strange to me - first of all, in header
of topic you are mentioning Plotter.Children, but in body of your question there are no words about it.
So I'll answer at all possible questions, that might be in your mind when you we asking it:
1) plotter.Children has a CollectionChanged event, which is raise when smth is added or removed in or to plotter.Children.
2) As Header is a simple ancestor of WPF's ContentControl, so Content property is a ContentControl.Content DependencyProperty. We can or cannot be notified about its change only if or if not developers of WPF's ContentControl created necessary
means. They don't. But don't be sad - there is a workaround of it:
DependencyPropertyDescriptor descr = DependencyPropertyDescriptor.FromProperty(ContentControl.ContentProperty, typeof(ContentControl));
This is a general way to be notified about change of every DependencyProperty.
3) Why do you need to be notified when the Content property has changed? You are setting it from your code, so every place in your code where you are changing its value can be a source of event. You might be in need of such an event if you are using Binding
or smth like that.
Have I answered on your question?