function get_child( $i ){
		return isset($this->children[$i]) ? $this->children[$i] : null;
	}
function get_child( $i ){
		return isset($this->children[$i]) ? $this->children[$i] : null;
	}
function get_child ( $ i ) { return isset ( $ this -> children [ $ i ] ) ? $ this -> children [ $ i ] : null ; }
Get child at given index
@param int
@return ParseNode
Get child at given index