datepicker with nested form field

Indeed, you will have to retrigger the datepicker plugin. You are probably doing something like

$('datepicker').some_function_to_do_your_datepicker_styling();

But of course, the dynamically added elements are not yet in the DOM.

So do something like:

$('form').on('cocoon:after-insert', function() {
  /* apply datepicker styling */ 
});