Couples who want to have a second child in the face of the new policy of balanced population development by fully liberalizing the second child, in addition to physiological preparation and adjustment of the family financial budget, must also be injected in advance with a psychological “vaccine” called the prevention of sibling rivalry. Sibling rivalry is, in short, an open and secret struggle between siblings in a large family for the possession of spiritual and material resources provided by parents and family members. At present, couples of the right age to have a second child happen to be the “post-70s”, “post-80s” or “post-90s” born under the one-child policy. Psychologically speaking, they have not experienced the pressure of sibling competition and have little opportunity to observe the living conditions of families with many children. When they have two children, they often simply use the “older one gives way to the younger one” approach when they encounter children fighting for favor or grabbing things between them. It is common sense for the oldest to give way to the youngest, but regular or unprincipled infringement of the oldest’s rights is not only unfair to the oldest, but also detrimental to the psychological growth of both children. For the oldest, it is easy to cause jealousy, splitting, rebellion, regression and other defensive psychology, which is detrimental to the perception of equality of personality and trust in others, and alienation from the family; for the second, it is easy to produce narcissism, dependence, shirking, projection and other defensive psychology, which is not conducive to the development of emotional intelligence, does not know how to share, difficult to establish good interpersonal relationships, and equally difficult to be self-sufficient in society. In the face of possible sibling rivalry, smart parents should give their oldest a good psychological “vaccination” before conceiving a second child. If the oldest is between the ages of 3 and 6, parents can tell him/her directly, in a very happy and slightly mysterious tone, “We’re expecting a little one!” Immediately the conversation turns: “You’ll be in charge of picking out the stroller.” The advantage of this is that it does not give the child the opportunity to react with rejection, but draws him/her directly into the “league” of welcoming a new baby and gives him/her some rights that he/she did not have before. This allows him/her to experience the positive energy of “I’m the oldest and I’m important” and to naturally accept the reality that he/she will have a younger brother or sister, laying a good foundation for future sibling harmony. If the first child is already in elementary or middle school, parents should be sure to talk to their child seriously and invite him or her to participate in decision-making before conceiving a second child. At this point, honesty and respect are most important. Don’t just talk about the good aspects, you must tell him/her truthfully: “With a younger sibling, mommy and daddy will have less time to take care of you, and I hope you will learn to take care of yourself and be able to help mommy and daddy with some things”. To take the oldest together to buy things for the second, decorate the room, but also from time to time to discuss with him (her) on the education of the future sibling views …… In short, so that he (she) understand that the addition of the mouth and his (her) choice is closely related, he (she) deserve to be able to take care of the second eldest brother (sister) and behavior example. There are some reports of a child threatening to leave home or to strangle a younger sibling as soon as he or she hears that the parents are going to have a younger sibling. The problem cannot simply be attributed to the one-child policy creating self-centered children, but rather to the parenting style of the parents. When a parent is incapable of raising a kind, sharing child, even if he or she does not have a second child, his or her personality is clearly flawed. If there is already such an oldest in the family, before parents are ready to have a second child, they should take the opportunity to reflect on their own educational philosophy and parenting methods, because parents who do not have obvious defects in their character and behavior will not have such a heartless and ungrateful child. In this sense, the “vaccine” should be given to the parents first.