Welcome to the forums, Lucyduke!
With regard to pregnancy books, the pregnant Sim will have a better pregnancy if she has read the pregnancy books. The better her pregnancy, the higher the chance that you'll be allowed to pick the baby's traits (as opposed to having them randomly assigned). In addition, there's a good possibility that she will get a wish (or even a few wishes) to read the book(s). Fulfilling those wishes will earn Lifetime Happiness points for her. Her partner may also get a wish to read the book(s). Or she (the pregnant one) may get a wish to have her partner read.
Many of the Childhood Development Books (as opposed to Children's general books) help with toddler skill-building when an adult reads the book to the toddler. If I recall correctly, those books will not help a child -- just toddlers. Adults may only read the books if they are reading to a toddler
OR if they have the Childish trait. Adults with the Childish trait can read these books and get credit toward their "Books Read" score.
As other posters have mentioned, recipes and musical scores are one-shot consumables, whereas skill books, fishing books, children's books, pregnancy and child development books and general inventory books are long-lasting.
One more note with regard to general inventory books: In addition to helping your writer, a non-writer Sim can benefit from reading them, especially if s/he has the Bookworm trait. Those books count toward your wishes to "Read X number of books". Your writer can also read any books s/he has written and they will also count toward "Books Read" (even though your Sim already knows how it ends
).
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Hmmm I could have sworn reading the books helped make for a happier pregnancy but I'll defer to Hosfac's info
, since I believe Hosfac has far more Sims 3 experience than I. Thanks for the clarification, Hosfac.
