How do I prevent the @children array from being changed outside the class since I only used attr_reader ?

attr_reader_issue.rb

class Human
  attr_reader :children
  def initialize
    @children = ["Joe", "Henry"]
  end
end
#=> nil
human = Human.new
#=> #<Human:0x2a19bd8 @children=["Joe", "Henry"]>
human.children << "Mary"
#=> ["Joe", "Henry", "Mary"]
human
#=> #<Human:0x2a19bd8 @children=["Joe", "Henry", "Mary"]>