django queryset to output foreignkey objects to ModelChoiceField

from django.forms import ModelForm, Select

class MyOtherModelForm(ModelForm):
    my_model=ModelChoiceField(queryset=MyModel.objects.all(), widget=Select(attrs={'style':'background_color:#F5F8EC'}))

    class Meta:
        model = MyOtherModel

Document.objects.filter(tagdb__tag_text__in=doc.tags_as_csv.split(' , ')).distinct()

class CustomCourseWidget(forms.Select):
    #http://djangosnippets.org/snippets/200/
    def render(self, name, value, attrs=None, choices=()):
        from django.utils.html import escape
        from django.utils.encoding import smart_unicode
        from django.forms.util import flatatt

        if value is None:
            value = ''
        final_attrs = self.build_attrs(attrs, name=name)
        output = [u'<select%s>' % flatatt(final_attrs)]
        output.append(u'<option value=""></option>') # Empty line for default text
        str_value = smart_unicode(value)
        optgroup_open = False
        for group in self.choices:
            option_value = smart_unicode(group[0])
            option_label = smart_unicode(group[1])
            if not ">" in option_label and optgroup_open == True:
                output.append(u'</optgroup>')
                optgroup_open = False
            if not ">" in option_label and optgroup_open == False:
                output.append(u'<optgroup label="%s">' % escape(option_label))
                optgroup_open = True
            if " > " in option_label:
                #optgroup_open = True
                selected_html = (option_value == str_value) and u' selected="selected"' or ''
                output.append(u'<option value="%s"%s>%s</option>' % (escape(option_value), selected_html, escape(option_label.split(" > ")[1])))

        output.append(u'</select>')
        return mark_safe(u'\n'.join(output))

self.fields['parent'].widget.value_from_datadict(
    self.data, self.files, self.add_prefix('parent')
)

from django.db.models import Q

children1 = Child1.objects.filter(blah=blah)
children2 = Child2.objects.filter(blah=blah)
parents = Parent.objects.filter(Q(child1__in=children1) | Q(child2__in=children2))