The children have "trained" Talia. She loves being allowed to join in their games, and willingly plays the parts assigned to her. Before she could walk, someone only needed to say "sit" and she would transform into puppy-mode, barking, fetching things thrown for her (in her mouth) and pretending to wag her tail. Now she has added baby to the list of roles she is well versed in.
She fake-cries for them to pick her up (which is either disturbing or hilarious, I can't quite decide which). When I voiced that thought, Jenna said, "Mum, it's a great thing. She knows that when babies cry, they get picked up and loved, no matter what."
(Off topic, in the babywearing picture of Jenna and Tali, look at the lovely Waldorf-y toy shelves in the background and you can play a game of spot-the-GUP!)