SIL (dh's brother's wife) is pg and due in.
September.
When they announced it I said I wasn't going to tell ds until twelve weeks because didn't want to have to tell him if anything went wrong.
After eight weeks they said that they were going to announce to everyone anyway so thought we should tell him. I didn't partly still because I didn't want to explain about mc if it happened but partly because he really won't be interested, or probably even remember. They live three hours away from us and we see them maybe once a year. I can't see that changing when the baby is born.
So although it's not a secret and we have talked about the upcoming baby in front of him, I don't plan to actually tell him until the baby is born that he has a new cousin.
If they lived closer it would probably be different, but he doesn't have a relationship with them really (through their own commitments/other things in their lives that mean they're never free), but he's not likely to see them before the baby is born anyway, and once it's born we will probably see them once and then maybe once a year as has been the case since he was a baby.
He is nine and other peoples' babies do not interest him at all.