K.A.
The only pregnancy of my 4 that we didn't tell the kids the day we found out was the only one that ended in miscarriage. It was actually harder to explain that I lost it because we waited so long. I lost it days after we told them.
We told them right away otherwise. My boys were 7 & 4 when I became pregnant with their sister. My oldest was a little over 2 when we told him I was pregnant with his brother.
It felt dishonest not telling them with the one we lost. If I didn't tell them with the others I would have had to explain why I was sick so much, so tired and going to the doctor. I just don't feel like lying to my kids like that. We took the older siblings to all the pre-natal appointments. I very often had to meet my husband at the birth center with my older kid as he worked down the road from it so we'd have a later afternoon apt and he'd leave work a little earlier that day.
They all did just fine. When I was pregnant with my third the boys were fascinated to learn where we were in development. We bought several books and even a couple of DVDs that they watched. They always had questions for the midwifes and they loved answering them. Even at 2 years old my son understood that mommy wasn't feeling well that day because it's a lot of work to grow a baby and can we just cuddle quiet on the couch. He loved driving his cars all over me LOL When I had my miscarriage the boys were amazing and understood that something didn't go right when the baby's body tried to grow so it couldn't be born and be a baby.
People really don't give kids enough credit in my opinion and shelter them too much from things they don't need to be sheltered from.