I told my kids pretty early, since I felt like they deserved to know before I told anyone else. My 7yo daughter is over-the-moon THRILLED. She's been asking about babies for at least a year now, and desperately wants a sister. She won't stop talking about it!!!! I kind of regret telling her so soon, lol. Every other second she's hugging my belly, asking a question (especially about when we find out it's a boy or girl, or what size the baby is *Right Now*, etc.), making a statement ("I can't wait until ____!"), or presenting me with things she's found around the house that she would like to give the baby. She even wants me to start a belly chart like I did last time, stuck to the bathroom wall (I told her no... just not into that this time around!!)
My 5yo son is also excited, and talks about "the new baby" frequently, has already decided it's a girl who will be named Mary, and is asking detailed questions. Like, exactly where the baby comes out when it is born. He used to hang around me when I went to the bathroom, he was invited to the homebirth of his brother, but I guess he was too young for all of that to stick with him. So I had to get out the baby books and show him graphic pictures before he was satisfied. He does like to know exactly how everything works. I guess I shouldn't have been surprised.
My youngest son is not yet three, so I don't think he fully realizes what we're talking about. He'll join on board with big brother and big sister and say "Yah. The new baby!" and stuff like that, but I don't see any comprehension in anything he says. I think he's in for a shock. He is STILL a complete mama's boy, and is very clingy and doesn't want daddy or grandma or anyone else to help when mommy is anywhere nearby... I think we'll have some jealousy issues to deal with when the baby is born.