Separation anxiety

Symptoms

Fussing and crying are the classic signs of separation anxiety. Screaming and tantrums are possible, too. During the day, your child may refuse to leave your side. During the night, he or she may wake up and cry for you.

Separation anxiety usually peaks between ages 10 and 18 months. Most children outgrow separation anxiety by age 24 months.

Causes

Separation anxiety is a normal stage of development for infants and toddlers. As your child realises that there's only one of you, he or she may become upset when you're not together — even if you just step into another room for a few minutes. Sometimes separation anxiety is triggered by changes in a child's life, such as a new child care situation, a new sibling or a new home. In other cases, family stress or tension may lead to separation anxiety.

References 

http://www.webmd.com/children/guide/separation-anxiety

http://www.medicinenet.com/separation_anxiety/article.htm

http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(14)62192-9/abstract

http://www.bmj.com/content/327/7407/158