A: Any time a new person is introduced into the environment (male or female) it is a big change for the child. At any age it is a challenge as a new “world order” is established but early childhood (3-6 years) and adolescence can be the hardest. Be mindful of how that persons parenting styles are different from what your child is accustomed to. Are there new things that he “can” and “can not” do when that person is around? Making slow transitions in changes is important (i.e. you should stay the parent in charge and continue to use the same discipline and reward techniques as you have in the past 3 years and make a slow transition to co-parenting over time). Try to create things that your son and the new person in the house can do together and have positive experiences (trip to the park, museum, ice cream) but be sure to also ask your son what things are important that the two of you need to keep doing together without the new person (bath time, bedtime stories, driving to day care). With time and consistency your son will adjust to the new situation. If his behavior continues to worsen or he has not adjusted within the next few months talk to your pediatrician about other resources.