Returns the object contained in the outer object's children if its attrName key and subsequent value matches the attrName and attrValue arguments provided.
Body
if (outer === undefined || !('children' in outer)){
return undefined;
} else {
return _.find(outer.children,function(child){ return 'attributes' in child && attrName in child.attributes && child.attributes[attrName] == attrValue; });
}