My daughter was 2.5 years old when we told her that we were having a baby. We got her a book called "Babies Don't Eat Pizz.a" that she loved. It talked a bit about what life with a baby is like (in toddler terms) so it helped prepare her for some things baby. When her little sister was born, she was a few months over 3 and we gave her a book called "Big Sist.er, Little Si.ster" that she loved as well which was more about all she can do as a big sister.
Re: recommend a new baby or big sister book
TTC #1: IUI #2 = BFP , Betas 550 (16 dpiui), 1523 (18 dpiui)
Hypothyroid, LPD, FSH 13.0, TTC 2 yrs B4 BFP
TTC #2: FSH 23, AMA, IUI 1, 2, 3 = BFN, IVF #1 = MC
IVF #2 = BFP - Betas 194 (14dp2dt), 366 (16 dp2dt), 841 (18 dp2dt)
(vanished twin ~7 weeks)