Hi Chok,
Congrats on the new arrival; new babies always bring good cheer!
As for the shunning; DO NOT WORRY YOURSELF; or upset your 5 year old child about it. My kids are a bit older and I think older kids could understand and cope with it. Tell the five year old that Auntie was not feeling well that particular day and could not stop to chat. End of story. The young ones buy anything you tell them and are usually satisfied. They could not understand the shunning.
Forget the bunch of them. We cannot justify why they do it, they will never accept our side of the story ; and so our lives are better off without them. Your former in laws will someday have to accept the consequences of their actions with your children; and you will have built a new life with a new spouse.
Good luck, Frank