It's only 5 years ago ;)

Right now my best option is properly to do a sort on the returning array my self.

I have debugged the Umbraco Controller to see if it is passing the right option values, and it is.

        /**
  * @ngdoc method
  * @name umbraco.resources.contentResource#getChildren
  * @methodOf umbraco.resources.contentResource
  *
  * @description
  * Gets children of a content item with a given id
  *
  * ##usage
  * <pre>
  * contentResource.getChildren(1234, {pageSize: 10, pageNumber: 2})
  *    .then(function(contentArray) {
  *        var children = contentArray; 
  *        alert('they are here!');
  *    });
  * </pre> 
  * 
  * @param {Int} parentid id of content item to return children of
  * @param {Object} options optional options object
  * @param {Int} options.pageSize if paging data, number of nodes per page, default = 0
  * @param {Int} options.pageNumber if paging data, current page index, default = 0
  * @param {String} options.filter if provided, query will only return those with names matching the filter
  * @param {String} options.orderDirection can be `Ascending` or `Descending` - Default: `Ascending`
  * @param {String} options.orderBy property to order items by, default: `SortOrder`
  * @returns {Promise} resourcePromise object containing an array of content items.
  *
  */
    getChildren: function (parentId, options) {
        var defaults = {
            includeProperties: [],
            pageSize: 0,
            pageNumber: 0,
            filter: '',
            orderDirection: 'Ascending',
            orderBy: 'SortOrder',
            orderBySystemField: true
        };
        if (options === undefined) {
            options = {};
        }
        //overwrite the defaults if there are any specified
        angular.extend(defaults, options);
        //now copy back to the options we will use
        options = defaults;
        //change asc/desct
        if (options.orderDirection === 'asc') {
            options.orderDirection = 'Ascending';
        } else if (options.orderDirection === 'desc') {
            options.orderDirection = 'Descending';
        }
        //converts the value to a js bool
        function toBool(v) {
            if (angular.isNumber(v)) {
                return v > 0;
            }
            if (angular.isString(v)) {
                return v === 'true';
            }
            if (typeof v === 'boolean') {
                return v;
            }
            return false;
        }
        return umbRequestHelper.resourcePromise($http.get(umbRequestHelper.getApiUrl('contentApiBaseUrl', 'GetChildren', {
            id: parentId,
            includeProperties: _.pluck(options.includeProperties, 'alias').join(','),
            pageNumber: options.pageNumber,
            pageSize: options.pageSize,
            orderBy: options.orderBy,
            orderDirection: options.orderDirection,
            orderBySystemField: toBool(options.orderBySystemField),
            filter: options.filter
        })), 'Failed to retrieve children for content item ' + parentId);
    },