I think I have it, but need to find a way to make it cleaner and that it will go down all the child items, children of children, etc... (in other words when you traverse really deep in the site).

@{
     var setCollapse = "out";
}

@if(@childPage.Name == currentPageName)
                {
                    setCollapse = "in";

                    @*<p>1 - childPage == currentpage : @setCollapse</p>*@
                }

                else
                {
                    setCollapse = "out";

                    @*<p>2 - childPage != currentpage : @setCollapse</p>*@
                }

                @foreach (var page in childPage.Children.Where("Visible"))
                {
                    if(@page.Name == currentPageName)
                    {
                        setCollapse = "in"; 

                        @*<p>3 - page == currentpage : @setCollapse</p>*@
                    }

                    foreach (var pages in page.Children.Where("Visible"))
                    {
                        if(@pages.Name == currentPageName)
                        {
                            setCollapse = "in"; 
                        }
                    }   

                }

                    <div id="@counter" class="panel-collapse collapse @setCollapse"> ... </div>