A new baby is a big change for everyone in the house, but the transition from a three-person household to a four-person household may cause the most turmoil for the firstborn child. You might be excited about the potential for your child to have a lifetime playmate, but he or she may not feel the same way. The baby might be seen as an intruder who sucks Mommy's time away from big sister or brother. But there are lots of ways to ease your child into sibling-hood, and the sooner you start getting him or her used to the idea, the better. The ways siblings adapt to new babies depends on a lot - mostly, their age. If the child is 2 or younger, then the only explanation you really need while waiting for baby's arrival is that the baby is growing in Mommy's tummy and will be here soon. That will work for awhile, but as the baby's arrival grows closer, the child may feel anxiety as he or she can't fit on Mom's lap anymore or Mom needs extra rest.