void paintChild(RenderObject child, Offset offset)

Paint a child render object.

If the child has its own composited layer, the child will be composited into the layer subtree associated with this painting context. Otherwise, the child will be painted into the current PictureLayer for this context.

Source 

void paintChild(RenderObject child, Offset offset) {
  assert(() {
    if (debugProfilePaintsEnabled)
      Timeline.startSync('${child.runtimeType}');
    return true;
  });

  if (child.isRepaintBoundary) {
    _stopRecordingIfNeeded();
    _compositeChild(child, offset);
  } else {
    child._paintWithContext(this, offset);
  }

  assert(() {
    if (debugProfilePaintsEnabled)
      Timeline.finishSync();
    return true;
  });
}