I tried to find a solution before and asked elsewhere but couldn't find the exact same issue. I have a parent game object that is a Rigidbody 2D, and this object has children that are BoxColliders 2D. (The parent object needs to be dragged, and the child blocks need to move along with it and to be colliders). It used to work in the past -- so i'm not sure if an Unity update broke this. But now my other Rigidbody 2D doesn't collide with these child BoxColliders any more.

Is there a (new ?) rule I don't know about using BoxColliders as child of a Rigidbody ? (or sometimes in the very same object)

By the way : I haven't assigned any material to the BoxCollider 2D and Rigidbody 2D, as I don't think they need it. The Rigidbody is Dynamic and I'd like to keep it that way.

Thanks for your help

  • \$\begingroup\$ No, there is no rule forbidding placing BoxCollider2D components on child objects of a Rigidbody2D or preventing resolution of collisions with such colliders. So your problem is elsewhere. Where, we cannot yet tell you, because you have not given us a Minimal Complete Verifiable Example. Edit your question to include every step a reader would need to follow to reproduce this problem in a new, empty project. Once we can reproduce the problem, we can test potential solutions to be sure they'll work for you. \$\endgroup\$
    – DMGregory
    Sep 26, 2021 at 17:35

1 Answer 1


Thank you DMGregory for your reply.

I [FIXED] it, the problem was really something else, so here it is, if that can be useful to anyone :

  • I tried with a backup of the project, and Unity 2018, no issues
  • I exchanged the scripts, gameobjects attributes etc. not working in Unity 2021
  • IN THE END, I tried unticking the checkbox Constraints > Freeze Position > Y (in the parent rigidbody of the child 2DCollider) which didn't cause any issues in the past
  • And it worked, the collider rigidbody coming from the top (Y) now collides as expected !

Have a nice day


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