In 1.13.0-beta.1 and above, the childViews array is not maintained (HTMLBars maintains a tree structure instead of a flat array listing).
I spiked getting things working for both pre-1.13 and post in this JSBin, snippet below:
didRender: function() {
function filterAttrMorphs(node) {
return node.constructor.name !== 'AttrMorph';
}
var childViews = this._renderNode.childNodes.filter(filterAttrMorphs)[0].childNodes
.map(function(node) {