title: Keep child object inside parent in Unity3D
body: <p>I have a <code>Collider2D</code> to make a border in my 2D game. I have another <code>Gameobject</code> inside this border and user can move it up/down by using a virtual Joystick .</p>
  
  <p>Now i want keep <strong>all of childs inside this border</strong> and when user move them <code>up/down</code> they dont go beind my special Border that is  a <code>Collider2D</code>.</p>
  
  <p>I have tried to do this before by using 2 <code>gameobject</code> on the top and down of my border for getting the position of them and check each the child objects but if i have more objects it's not a good idea.</p>
  
  <p>What i want to do is like bellow picture</p>
  
  <p><a href="https://i.stack.imgur.com/1YvEl.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1YvEl.png" alt="enter image description here"></a></p>
  
  <p>How i can do this ? </p>