Inline formsets - How to set default values for child form

I have an inline formset factory with a Parent entity and a child entiy.

I need to set the child form initial values depending on the parent's attributes.

I thought that doing this in the init of my BaseFormset form would be the best way.

So here's what I do:

class MyBaseFormset(BaseInlineFormSet):

def __init__(self, *args, **kwargs):
    #Crispy
    ...
    super(MyBaseFormset, self).__init__(*args, **kwargs)

    form = self.forms[0]
    temp = Child()
    temp.x = "a"
    temp.y = "z"
    form.instance = temp

The first time I executed this it seems to work - but now I always get an empty/default form for my child.

Any ideas what I might be doing wrong? I don't get any errors...

Sometimes you don't see the wood because of all the trees...

Just use inital value and not an object:

form.fields['x'].initial = self.instance.x