I'm using the Kendo UI Web v2012.1.515 version and had a need to expand the first item in a dynamically created PanelBar (in code behind via c#). To make it more complicated, I'm working in SharePoint 2010. After sniffing around the DOM for a bit, I found a class on the first item in the panel "k-first". Since accessing the PanelBar.expand() method requires a jQuery selector, I decided to use this class as my selector...
here's the code snippet...

//pass the PanelBar into a JavaScript Object...
var ScorecardList = $("ul[jqID|='ScorecardList']=").kendoPanelBar({ });

//Show the first Item in the DisplyOrder Option List...via the k-first class...
var FirstExpand = ScorecardList.data("kendoPanelBar").expand($(".k-first"));

Disclaimer...this worked for me. This might not work in future releases, and may not work as described here. Your mileage may vary.

Hi Joey,

You can also omit the $() or use expand("> li:first") as a selector (to be sure it is the first descendant of the PanelBar root).

Also, please note that expand() will return the PanelBar object, not the item.

Regards,
Kamen Bundev
the Telerik team

and how can i select the son item for the first root item?

Hello eliraz,

You can use:

I hope this will help.

Regards,
Alexander Valchev
Telerik