If you don’t think it is a big deal to be replaced by a baby brother after being the princess of the household and the apple of daddy and mommy’s eyes for 2 or more years,
try to put yourself in your child’s place.
Imagine: You have been happily married for 2 or more years and your husband treats you like you are special and wonderful. One day he says, “Guess what, I’ve decided to bring home another wife. I’m so happy about getting another wife and I’m sure you will be too. We will all be one big happy family.” You get the picture.
When the new baby arrives, both parents are exhausted and sleep deprived. Mom may be breast feeding which takes a lot of time and energy. Mom holds the baby close and quickly comforts the baby when he cries. Dad certainly plays with baby’s two year old sister, but may seem to have less energy and patience. Maybe your toddler is getting a little less outside play time. Your toddler may perceive correctly that she is getting less attention and baby gets a lot more.