How do I create objects with nested items using serializers in Django REST

I want to create a caretaker. This is my model:

class Caretaker(models.Model):
    user = models.OneToOneField(User)
    language = models.ForeignKey('Translation', blank=True, null=True, on_delete=models.SET_NULL, verbose_name=_('language'))
    patients = models.ManyToManyField('Patient', through='CaretakerPatient')
    specialists = models.ManyToManyField('Caretaker', through='CaretakerSpecialist')
    name = models.CharField(_('name'), max_length=50)
    email = models.CharField(_('e-mail'), max_length=100)
    time_zone = models.CharField(_('time zone'), max_length=50)
    is_primary = models.BooleanField(default=False)
    active = models.BooleanField(default=True)

As you see there is a relation oneTOone with django.contrib.auth.models.User.

My API view is the following

@csrf_exempt
@api_view(['POST'])
@renderer_classes((CustomJSONRenderer,))
def create_user(request):
    serializer = CaretakerSerializer(data=request.data)
    if serializer.is_valid():
        serializer.save()
        retu Response(serializer.data, status=201)
    retu Response(serializer.errors, status=400)

My Serializer classes...

class UserSerializer(serializers.ModelSerializer):
    class Meta:
        model = User

class CaretakerSerializer(serializers.ModelSerializer):
    user = UserSerializer()
    language = serializers.SlugRelatedField(slug_field='language_code', read_only=True)
    time_zone = serializers.StringRelatedField()

    class Meta:
        model = Caretaker
        fields = ('id', 'user', 'language', 'name', 'email', 'time_zone', 'active')

    def create(self, validated_data):
        print validated_data
        user = User(
            email=validated_data['email'],
            useame=validated_data['useame']
        )
        user.set_password(validated_data['password'])
        user.save()
        caretaker = Caretaker.objects.create(**validated_data)
        retu caretaker

My question is: sending data like:

{'useame': 'xxx', 'password': 'xxx', 'email': 'xxx@xxx.com', 'name': 'John Smith' ... }

How can I split useame and password in order to create first the user, and then use this object to create the caretaker? The validated_data just gave me the fields of the caretaker model.