How can we call child component controller method from the parent component controller method in Salesforce?

hii,

Syntax to call Child Component in Parent component is :

<c:childComponent aura:id=’childCmp’ />             – Use this Syntax if no namespace is defined by you.

<yourNameSpace:childComponent aura:id=’childCmp’ />   Use this Syntax if you have your own  namespace is defined by you.