Can you imagine coming to life to two grown sons? Two incredibly capable sons, who are also very good looking (stop it, don't pretend you didn't imagine that part), and who are always in constant trouble? It has to be difficult for Mary to come to terms with what has become of her family.
Cas is still on the job, you guys! Riding with an entirely new Winchester family. He pretty much as seen it all, hasn't he? I wonder if he ever looked down and saw the full picture with the little ones, BEFORE Mary was barbecued on the ceiling.