It certainly is a phase. Most kids at 2 are exploring their growing independence. They're noticing they have new motor skills that allow them some freedom to explore their environment, and finding they have strong preferences but little ability to regulate their emotions. One of the reasons why we have the phrase "terrible twos" is that this is commonly when a child's capability for exploring the world is clashing with the rules of the world.

Every family with a two-year-old may experience acting out—the child doesn't want to put on his shoes, or he doesn't want to go to bed one night a week, so there's a lot of screaming. But if it's happening every morning as you go out, or the house ends up looking like a disaster area, or it happens every night for bedtime, or it takes hours to get the child to bed, and parents are pulling their hair out and no one is sleeping—that is when professional help may be necessary.

I often tell parents about a clinical acronym we use to better understand whether a child's symptoms are consistent with a mental health diagnosis: FIDI, for "Frequency, Intensity, Duration and Impairment." When parents come into the office worrying about a child's tantrums, I ask, "How often do the tantrums happen? How intense do things get? How long do these things last and how long have they been going on? How much does it get in the way of you being able to do stuff as a family?" We have diagnostic criteria for certain behavior disorders, but those criteria don't cover every behavior that could impair a child's or family's functioning. So we have to look objectively at the frequency, intensity and duration of these behaviors, and then discuss how they're impairing the child's life and family.

Impairment is the key dividing line between "typical" and clinical, and it isn't always as sharp as we would like it to be. It may be that a child has milder behavioral issues, but they are really getting in the way for a family and causing a lot of conflict between the parents. We don't only treat problem behavior if it is the most severe it can be. We treat because a family needs help.

Parents are not necessarily the cause of behavior problems, but they can be the solution. Behavior problems have many different causes. There are biological and genetic reasons why a child might have behavioral difficulties. Some children react more strongly to interruptions in daily rhythms - like overreactions to hunger or irritability related to too little sleep. Some children have real difficulties controlling emotions, difficulties that have been there since infancy as part of a reactive and highly sensitive temperament.

To be sure, there are parent-child interaction patterns that we know lead to a higher instance of behavior problems—usually the techniques we would call "harsh discipline." Parents who end up making threat after threat, who engage in physical discipline, or who frequently criticize their children often see more behavior problems.

But the issue we see most often is parents who believe their child's behavior problems must be the result of their actions or some mistake in discipline, like being too harsh or too permissive. The reality is it can happen to anybody, and we want to re-establish a balance between nurture and structure in effectively managing behavior. We see parents who have what seems to be flawless parenting strategies with one child in a family, and through no fault of their own, the other child has just stumbled upon ways of coping with stress or with their emotions that become impairing and disruptive over time. Parenting is just a part of what goes into a child's behavior patterns; but parent behavior is adjustable, so it's one of the most powerful tools we have.

There is no FDA-approved medication for oppositional defiant disorder (ODD) or conduct disorder (CD), the diagnoses that apply to this sort of behavior, but medications are sometimes used as an adjunct to behavioral therapy. Frequently, children with ODD also have a diagnosis of ADHD. Stimulant medication may be used if a child has difficulty paying attention to adults, following directions or exhibits excessive impulsivity. Antidepressants may also be helpful if a child has underlying depression or anxiety that may be contributing to irritability or problems regulating emotions.

First of all, it's good that he's not having these problems in school. That allows us at least one setting where we don't have to intervene. Somehow, aggression is leading to some payoff with his brother, whereas in school, either the boundaries are there or aggression against peers doesn't get the same payoff, and he doesn't demonstrate these extreme behaviors.

Now we have to address this sibling rivalry, which sounds like it is out of developmental proportion and more severe. But here's the catch: it has to be behavioral intervention for both of your sons. Even if one sibling is the "patient" who causes a lot of the conflict, we also have to teach the other sibling how to stay emotionally regulated in the face of provocation, that there is a payoff related to getting along with their brother or sister. What that means is that we're going to do the same kind of behavioral parent training interventions, but we're going to apply reinforcement for positive behaviors to each sibling, and we're going to implement specific consequences for misbehavior even when you may never be sure of the truth of some of the sibling's accounts. It becomes a little more complex in that way, but over time, siblings should see that there is more reward in getting along and working out their differences together.

Evidence-based practice for treating oppositional defiant disorder (ODD) involves behavioral parent training. This can come in a number of different forms, such as Parent-Child Interaction Therapy (PCIT) and Parent Management Training, or group interventions like Incredible Years. However, the underlying principles are the same: focus on fortifying a positive relationship with the child, clearly define behaviors that parents would like to change, reinforce and amplify positive behaviors, withdraw attention from certain minor misbehaviors, and sparingly but consistently use appropriate punishment for major misbehavior. In general, behavioral parent training takes from three to five months. Parents usually see significant changes as they're applying the strategies, even in the first month. But it can take three to five months for the entire course.

For many of these treatments, the "graduation criteria" are that parents report a child's symptoms are approaching what we would consider the typical range, that parents have confidence managing their child's behaviors, and that we've decreased impairment across settings. That doesn't necessarily mean it's all gone away. For many parents there's still a sense that as the child reaches new developmental stages, those boundary-pushing impulses might again present themselves, and we may need to have booster sessions to help the family manage this new phase.

Adolescents are constantly balancing how independent they feel they should be with how independent they actually are. It can be very irritating to feel like you've now heard your parents say the same thing thousands of times even though you're mature and you know what you're doing. So, the first possibility is that your daughter is just being a teenager. Now it's just about focusing on how to maintain the relationship with her so you can all survive adolescence.

The second possibility is that these are real, impairing behavioral issues that have unfortunately come out of the blue, and you might need some help. In my experience, the best tactic for parents of argumentative teenagers is to come up with a list of a few non-negotiable rules for desired behavior and link the teen's behavior to her privileges. You want your teen to understand the following mini-speech, "We're trying to give you your freedom, but we require certain things just to be a member of our household. If you are able to follow through on these things, then you will get some of the privileges and independence that you're looking for."

Finally, it's important to mention that a hallmark of depression in children and adolescents is irritability. Adolescence is a time when teenagers may be much more prone to depression than children or adults. This is a major issue that we want parents to understand, and in this case we want to help parents to be vigilant in watching for other signs of depression, including persistent sadness, sudden decline in school performance, losing interest in activities she used to enjoy, irregular sleep patterns and sudden weight loss or gain.