DS knows. Yesterday morning he woke up and said, Mommy I think there is a baby in your tummy. When I asked him why he thought that, he told me he dreamed it and he has been wanting a baby brother and sister for a long time. So I confirmed that there was a baby and he was so happy, he had to call his grandparents to tell them (they already knew but he wanted to tell them too).
Unfortunately, he is so excited he can't keep it to himself. We went out to dinner last night with DH's family and I told his aunt. DS overheard and decided everyone needed to know and started telling everyone including some random stranger who was standing by us, There is a baby in my mommy's tummy.