addChildren
Adds each of children as a direct child of this node, in order, validating each one the same way as addChild.
Validation is performed per node as it is added, so if one node fails the children added before it remain attached (the same partial-application behaviour as calling addChild in a loop).
Parameters
children
nodes that are not already attached to a tree.
Throws
if any node already has a parent, or if attaching it here would create a cycle (i.e. it is this node or one of its ancestors).