Don't add that child control to the panel, add it to the control that should be the parent:
HtmlGenericControl divcontrol = new HtmlGenericControl();
divcontrol.Attributes["class"] = "sxro sx1co";
divcontrol.TagName = "div";
pnlUserSearch.Controls.Add(divcontrol);
Label question = new Label();
question.Text = "text";
divcontrol.Controls.Add(question); // add to the new div, not to the panel