I wonder if there is any single child who has not been jealous of a newly born sibling. It is quite normal for a child to feel jealous of the new baby because it is the first time in a while; he has seen his beloved mama hold a new baby with the same love and care he used to get before the arrival. The jealousy between siblings can be easily managed with the right amount of love and attention. Your prime goal to handle this situation is to help your child manage his emotions so that love gets the chance to grow and wins the situation.
The first thing you as a mother need to do is to prepare your child mentally while you are still pregnant. You need to get your baby excited about the arrival of the new addition to the family and tell him that he is going to get a new brother/sister with whom he can share love and toys and with whom he is going to share the bond of affection and love for the rest of his life. Ask him to pick clothes for the newborn and help you set and paint the baby's new room. You need to make your child feel connected to the baby even before he/she is born.
During birth, you must make sure that your elder child doesn't feel left out and abandoned. Having his beloved mama vanish to the hospital and only getting back with a new baby held in arms is the stirring event of jealousy between siblings. The whole situation can traumatize your little kid and make it difficult for him to welcome the newly born. Instead, when you arrive at home, make sure you go straight to your older child and hug him tight and do a lot of adoring kisses. Make it about your reunion with him and not with the newborn.
But despite all you do, your older child, at some point, is sure to face the reality of his beloved mama now going away from him and giving all her love and attention to this new baby on her lap. But this also can be managed by giving him extra love and affection, staying calm, and being supportive. You need to get him involved in helping you with the new baby. Ask him to sprinkle some powder on the baby while you change the diaper or teach him to put socks on his little brother/sister’s tiny feet. Don’t forget to praise and encourage him whenever you get the chance.
Most importantly, teach your older kid to be gentle with the new baby. It is not convenient to leave the two alone, and if you are going for a constant string of 'Nos' with the older child, you need to remind yourself that it will only make things work. Be patient and calm. Things will work out, and you will be a happy family again!