在panel的派生类中找不到children会合

在panel的派生类中找不到children集合
大神求助，
代码（片段）

 public partial class uniformstack : Panel
  {

  protected override Size MeasureOverride(Size availableSize)
  {
  if (Children.Count == 0)
  return new Size();
  Size availableChildSize = new Size();
  Size maxChildSize = new Size();
  Size compositeSize = new Size();
  if (Orientation == Orientation.Horizontal)
  {
  availableChildSize = new Size(availableChildSize.Width / Children.Count,
  availableChildSize.Height);
  }
  else
  {
  availableChildSize = new Size(availableChildSize.Width,
  availableChildSize.Height / Children.Count);
  }
  return base.MeasureOverride(availableSize);
  }
}
children下面一直是红线。显示“当前上下文不存在名称children”

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同样的代码我这里是正常的
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me too
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我这里倒是 if (Orientation == Orientation.Horizontal)出错