my baby girl is 3year 8month old now I have baby boy 2month old ...after my second baby my girl get too changes in her behaviour... stubbornness is much increase compare to before my second baby...how can I understand my first baby's behaviour and mind set

A. It’s common to be seen when you do not prepare an older one for a younger sibling to come and once a sibling comes you know you spend more time with them pay more attention to them so the older one usually gets jealous and left out so you need to teach your child that this one’s your younger sibling you have to play with the one you have to help me to bring the child up you are still my more important priority but this one doesn’t know how to do anything on its also I have to take more or extra care of the person try to make the child comfortable with the process and a part of the upbringing of the younger one