children(function(el) {
      var a, b, c;
      a = input(props({ type: 'email' }));
      el.email = a;
      // etc
      return [a, b, c];
    })

Entirely guesswork but: El is the form element you're defining children on. You need to provide references to the elements you're creating so that you can use them later (el.email and friends) but you also need to return them to the children function in an ordered manner so that it can actually attach them into the DOM.