Sizes a bounding box to its children.

bounds.cs

BoxCollider collider = gameObject.AddComponent<BoxCollider>();
Bounds parentBounds = new Bounds(Vector3.zero, Vector3.zero);
Bounds childBounds = new Bounds(Vector3.zero, Vector3.zero);

MeshFilter[] meshFilters = transform.GetComponentsInChildren<MeshFilter>();
foreach (MeshFilter meshFilter in meshFilters) {
  childBounds.center = transform.InverseTransformPoint(meshFilter.renderer.bounds.center);
  childBounds.size = meshFilter.sharedMesh.bounds.size;
  parentBounds.Encapsulate(temp);
}

collider.size = bounds.size;
collider.center = bounds.center;