Parents should have an in-depth conversation with their child's caregiver about the baby's arrival and work in partnership to help a child adjust to a sibling. A child's daycare setting, where he is among friends and a familiar setting, often becomes a "safe" place where a child acts out his true feelings over the situation. Daycare is also a place where not everyone will ask him about his "new little brother or sister" and discuss how excited he must be. Parents also tend to push the "love your little brother/sister" and to pose in pictures or lovingly hold the baby, when the reality is that the toddler or youngster truly doesn't want to. Preschool/daycare provides a place where those conversations won't be centered on the baby or an onslaught of photos taken with. Daycare also lets the older child be just like he/she was BEFORE the baby, something that most kids struggling with a new baby find reassuring.
Caregivers are familiar with a young child's emotions on this matter and can help a child to face angry feelings over "not being the primary focus" any longer with mom and dad. Providers can also livingly talk with a youngster on how to express feelings rather than suppress them at daycare and learn to feel in control of them and then move on.
Early educators will also know to be on the lookout for any unusual or atypical behaviors of a child and deal with the actions while understanding the motivation behind them. That can change how a child is talked with or even disciplined, if needed. A "big brother" who suddenly starts biting or a new "big sis" who scratches her friend may be acting out, but the child must also understand those are never acceptable behaviors, and other ways to unload stress or to express themselves must be found. Together, the caregiver and child should be able to find a solution that provides the outlet without harming others. (An example that works with one child care provider is to let the child run around the backyard three times--supervised, of course--whenever the urge to feel stressed strikes.) That self action encourages the child to also start to sense when she is beginning to feel out of control, and a way to bring the emotions back in check, according to the provider.
Daycare providers may ask parents to check in with them prior to dropping off a child on a daily or frequent basis to go over any behavioral issues, which could even include regressing to babylike gestures and mannerisms like the new baby. Certain games or role playing can be initiated where all kids in the classroom can act out being a big kid or young baby and how the abilities, actions and behaviors are same or different. Letting a child talk about how he/she will help the baby to do certain things or plans for teaching an infant to walk and eventually play ball can also help.
Parents should understand that their darling toddler may act one way at home and then a completely different way anywhere else, and avoid being surprised, defensive, or accusatory over wide swings in behaviors. The more they can stay compassionate and calm, including their older child in quality time both with and without the baby, and maintain any family rituals will help in the long run.
One family celebrated an older child's maturity by moving bedtime 15 minutes later, and made it a big ritual as to how he got to stay up with mom and dad while baby had to go to bed. The time difference in bedtimes will remain different through the children's elementary years to help reinforce the role of the "older, more mature" child. Similarly, preschools can take measures (even if mostly symbolic) to let the older child demonstrate a skill or knowledge to everyone else or having the child perform a special task in the baby room that lends his/her newfound expertise.
In the end, the best advice is to give a child an outlet to express and work through feelings and not feel forced to pretend or suppress emotions, and then communicate often with other adults who care for a child with a new brother/sister to find ways to put the positive attention on a formerly only child (or whatever the changed family arrangement is). In the end, the best advice remains true: "Give it time!"

