Getting the correct list of objects

If I can have one more question (these are my first days with Python and Django)
I have three models:

class Guardian(models.Model):
    guardian_first_name = models.CharField(max_length=50, verbose_name='Imię opiekuna')
    guardian_last_name = models.CharField(max_length=100, verbose_name='Nazwisko opiekuna')
    guardian_login = models.CharField(max_length=50, verbose_name='Login')
class Baby(models.Model):
    class Meta:
        verbose_name_plural = 'Babies'
    first_name = models.CharField(max_length=50, verbose_name='Imię') 
    last_name = models.CharField(max_length=100, verbose_name='Nazwisko')
    date_of_birth = models.DateField(verbose_name='Data urodzenia')
    sex = models.CharField(max_length=12, verbose_name='Płeć')
    height = models.PositiveIntegerField(verbose_name='Wzrost')
    weight = models.DecimalField(verbose_name='Waga', decimal_places=2, max_digits=5)
    guardian = models.ForeignKey(
        Guardian, on_delete=models.CASCADE, verbose_name='Opiekun', null=True, default=None, blank=False)
class Activity(models.Model):
    class Meta:
        verbose_name_plural = 'Activities'
    date = models.DateField(verbose_name='Data')
    start_time = models.TimeField(verbose_name='Czas rozpoczęcia')
    end_time = models.TimeField(verbose_name='Czas zakończenia')
    baby = models.ForeignKey(
        Baby, on_delete=models.CASCADE, verbose_name='Dziecko', null=True, default=None, blank=False
    activity_type = models.ForeignKey(
        Activity_Type, on_delete=models.CASCADE, verbose_name='Rodzaj aktywności', blank=False, default=None, null=True

The Guardian object that is logged in has children who have their own activities. And I would like to download the activity list, but only his children. I have the guardian’s id so I download the list of his children
I am also downloading a list of all Activities
activity_list = Activity.objects.all().order_by('-date', '-start_time')
How do I filter the queryset activity_list now so that it only leaves me there activities that are children from queryset baby_list?
Thank you

Take some time to read all of Related objects reference | Django documentation | Django.

If you have an object of type Guardian, perhaps named my_guardian, then the set of Baby related to my_guardian is my_guardian.baby_set.all(). The baby_set in this case is a manager, which means you can also apply a filter. For example, my_guardian.baby_set.filter(height__gt=36) would return the set of Baby associated with my_guardian with a height field containing a value greater than 36.

Since Activity is related to Baby, then the same logic applies. For each instance of Baby, the set of Activity related to it is accessible through the activity_set manager.