Issue90Parent p = new Issue90Parent();
p.setName("First Parent");
pm.makePersistent(p);
Object id = pm.getObjectId(p);
Issue90Child c1 = new Issue90Child();
c1.setName("Child 1");
Issue90Child c2 = new Issue90Child();
c2.setName("Child 2");
p.setChildren(Arrays.asList(c1, c2));
pm.makePersistent(p);
pm.close();