There’s a House Inside My Mommy by Giles Andreae (illustrated by Vanessa Cabban; Albert Whitman, 2002) is the perfect balance between a technical “how a baby grows” and exciting “a baby is coming.” Told in rhyme, this book doesn’t have sketches of the life changes for an older child when a new baby comes, and it likewise does not explain how a baby is grown. It’s written for children who may not know what’s going on.
There’s a House Inside My Mommy captures daily life for a child with a pregnant Mom: Mom feels sick, Mom falls asleep a lot, child talks to the baby through Mommy’s “tummy telephone” (My 4-year-old son loved that part). Of course, in the end, a baby joins the family. The emphasis in Mr. Andreae’s book is on the long process of pregnancy, and my son and I enjoyed reading the rhyming story so similar to our own. Also, the child in this book is illustrated in a way that it can be interpreted as a boy or a girl, so that may be a nice touch for you to adapt the story to your own situation.