Siblings fight with one another. They argue, they fuss, they complain about one another. As parents, we hear it all the time, "Mommy, he took my doll," "Daddy, she is being mean to me." Sometimes we referee to settle an argument; sometimes we let our children work it out together. A certain amount of sibling disagreements are to be expected. After all, it is impossible to live with someone all day, every day, without having different opinions. We come to accept that our children will fight with one another on occasion. But when does it cross the line and become bullying?
Bullying is defined as "the process of intimidating or mistreating somebody weaker or in a more vulnerable situation."
And bullying, we know, causes long-term damage to its victims - anxiety, depression, PTSD, lower self-esteem. We usually think of bullying occurring in school or on the playground and more recently in the cyber world of social media, but bullying also occurs in our homes - among siblings.
A recent study, completed at the University of New Hampshire, showed that when bullying occurs at home, between siblings, the effects are the same - victims experience mental distress. Researchers conducted more than 3,500 telephone interviews with children and teenagers, or caregivers when the child was less than 10 years old. The children and teens were asked questions about physical assault, property damage, name calling, meanness and ostracism by other siblings.
Some of the results of the interviews:
- Children and teens both reported mental distress from bullying by siblings - even when bullying occurred once in a while.
- Younger children (younger than 10) were at a higher risk of mental health effects from mild bullying
- About one-third of the children and teens interviewed said they had been bullied in some form by a sibling in the past 12 months.
According to Corinna Tucker, the author of the study, "Even children who experienced just one type of sibling aggression had worse mental distress than with a child who experienced no sibling aggression. There has been a lot of work to prevent or stop aggression for peers, but not much is seen for sibling aggression." 
Difference between sibling rivalry and sibling bullying
How do parents know what is normal childhood rivalry and bullying? Life Counseling Solutions in Maitland, Florida explains that when you were young, "you argued over who the best athlete is or constantly fought over who would ride in the front seat."  But this isn't necessarily sibling bullying. "Sibling bulling is different from sibling rivalry in that its main purpose is to hurt the other child"physically or emotionally."  According to the counseling center, the warning signs of sibling bullying are:
- Harsh insults such as "you are fat (ugly) (stupid)" or "you aren't good at anything" or "no one likes you"
- Physical aggression such as hair pulling, hitting or pushing
- Destruction of the other siblings toys
- Ganging up of two or more siblings and not allowing them inside or blocking their way
Some suggestions for parents to help prevent sibling bullying include;
- Watch your children while playing to assess how they get along
- Spend one-on-one time with each child
- Talk as a family about how to treat one another
Children learn relationship and conflict resolution skills from their parents. Your children will pay attention to how you work out conflicts with your spouse, your siblings and each of them. If you work through disagreements with respect, your children will follow your lead. The Great Lakes Psychology Group states, "Parental and adult intervention teaches children how to start that dialogue and work through emotions to identify why they are doing what they're doing and how exactly they feel. Parents are the "coach," showing them how to properly handle new and challenging situations and navigate the murky world of burgeoning emotions." 
 "4 Warning Signs of Sibling Bullying," 2013, July 1, Scott Thigpen, Life Counseling Solutions
 "Bullying Among Siblings - Not as Harmless as We Think," 2013, June 17, Lynn Nguyen M.D., ABCNews
 Definition: Bing Dictionary
 "Sibling Bullying - Beyond Normal Rivalry," 2013, July 3, Tricia Stehle, Great Lakes Psychology Group
"Sibling Bullying Associated with Anxiety, Depression in Victims," 2013, June 17, Staff Writer, Medical News Today