class ChildModelInlineAdmin(admin.TabularInline):
    # Here you can specify a number 
    # of additional inlines (extra) for add_view.
    extra = 3
    model = SomeModel


class SomeParentModelAdmin(admin.ModelAdmin):
    inlines = (ChildModelInlineAdmin,)

    def get_formsets(self, request, obj=None):
        for inline in self.inline_instances:
            fs = inline.get_formset(request, obj)
            if obj:
                # Here you can specify a number 
                # of additional inlines (extra) for change_view.
                fs.extra = 0
            yield fs