{ parse: true } not passed to children

gistfile1.js

var State = require('ampersand-state');

var A = State.extend({
  props: { n: 'number' },
  parse: function (attrs) {
    attrs.n = parseInt(attrs.n, 10);
    return attrs;
  }
});

var B = State.extend({
  children: { a: A }
});

// parses string to int
var a = new A({ n: '1' }, { parse: true });

// throws TypeError
var b = new B({ a: { n: '1' } }, { parse: true });