these 2 questions are all about attachment theory, the evidence base. of course there is lots in the eyfs about it, key PERSON etc.
you need to read bowlby , mary ainsworth and cassidys the nature of a child's ties ( i think thats the name from memory)
use this page as a pointer
http://en.wikipedia.org/wiki/Attachment_in_children
but NEVER use wikipedia as a reference it is unsound
evidence base means research.