Surely he'd talk by three. When three came and went, it was surely four. It was a never ending cycle of "everything will be different next year."
A family is made up of many people. While no member should be raised above others to define you all, no member should hidden in the shadows either.
I can't pretend to know the tone of their curiosity, but I'm sure it's there and it really balances out to, "What must it be like when they're all alone back at home?"
Lucas may be able to recognize some words and directions but, as a non-verbal five year old, the concept of "bless you" isn't one of them.