Much of the age regression issues depend upon the age of the older sibling when the baby is brought home. Children under the age of four tend to have the greatest difficulty with the birth of a sibling. This is because they lack the developmental awareness or experience to make sense of the new addition to the family and title of “big brother/sister.” These titles tend to have little meaning to them, so they are more surprised and distressed by the experience.
In addition, toddlers and preschoolers are in the midst of a number of developmental changes or have only very recently completed numerous developmental tasks, so they are most vulnerable to regression.
Sleep.
Young children who have been sleeping through the night may suddenly be up and out of bed during midnight feedings with the newborn baby. They are likely working through uncomfortable feelings that may disturb their sleep cycle. They may, unconsciously, wish to join their parents in the middle of the night to get that much desired attention and comfort that they have been missing since they had to split time with the new baby.
Potty Issues.
Young children may become distracted by the new baby and forget to make it to the potty. They may also wish for a simpler time in their life when they received extra time with mom or dad on the changing table.
Feeding.
Moms who breastfeed may find their older child trying to crawl into their lap, hang from their arms or shoulders, nudge the new baby while nursing, or ask to nurse themselves. Similarly, older siblings may ask for a bottle and/or pretend to suck from a bottle.
It can be very difficult to tolerate seeing the intimacy of the connection and the time spent between a parent and the newborn, and the older sibling may very well want to be included in the attention.