How to skip vars_prompt if variables exist within import_playbook?

I have this playbook script to execute some basic task on the switch and firewall.

Requirement :

• Case 1. User need to execute the parent script to perform all basic task on child 1 and child 2.
• Case 2. User need to execute directly on the child 1 to perform basic task.
• Case 3. User need to execute directly on the child 2 to perform basic task.

Information :

• Parent script host only localhost.
• Child 1 script hosts are multiple switch.
• Child 2 script hosts are multiple firewall.

Parent : test_dummy_sw_fw.yml

- hosts: localhost
  become: no
  gather_facts: no

  vars_prompt:
    - name: ansible_user
      prompt: "Enter Username"
      private: no
    - name: ansible_password
      prompt: "Enter Password"
      private: yes

- name: Execute Script on Switch
  import_playbook: test_dummy_sw.yml

- name: Execute Script on Firewall
  import_playbook: test_dummy_fw.yml

Child 1 / Switch : test_dummy_sw.yml

- hosts: Switch
  become: no
  gather_facts: no
  
  vars_prompt:
    - name: ansible_user
      prompt: "Enter Username"
      private: no
    - name: ansible_password
      prompt: "Enter Password"
      private: yes
  
  tasks:
    - name: Interface Config
      ios_config:
        lines:
          - description Testing Switch
        parents: "interface Gi0/0"  
      register: print_output

    - debug: var=print_output

Child 2 / Firewall : test_dummy_fw.yml

- hosts: Firewall
  become: no
  gather_facts: no
  
  vars_prompt:
    - name: ansible_user
      prompt: "Enter Username"
      private: no
    - name: ansible_password
      prompt: "Enter Password"
      private: yes
  
  tasks:
    - name: Interface Config
      asa_config:
        lines:
          - description Testing Firewall
        parents: "interface Ethernet1"  
      register: print_output

    - debug: var=print_output

I want to create a script to skip the prompt when a variable has been set in a parent playbook. I've also tried this on the playbook, but Ansible still prompts for the variable in the child playbook.

Parent :

- hosts: localhost
  become: no
  gather_facts: no

  vars_prompt:
    - name: ansible_user
      prompt: "Enter Username"
      private: no
    - name: ansible_password
      prompt: "Enter Password"
      private: yes

  tasks:
  - set_fact:
      ansible_user: "{{ ansible_user }}"
      ansible_password: "{{ ansible_password }}"

- name: Execute Script on Switch
  import_playbook: test_dummy_switch.yml
  vars:
    ansible_user: "{{ ansible_user|d('default') }}"
    ansible_password: "{{ ansible_password|d('default') }}"
        
- name: Execute Script on Firewall
  import_playbook: test_dummy_fw.yml
  vars:
    ansible_user: "{{ ansible_user|d('default') }}"
    ansible_password: "{{ ansible_password|d('default') }}"

Is there any way to ensure that Ansible recognizes that the variable already exists and skips the prompt without using extra variables ? Because the requirement of this script are only needed to prompt once for username and password.

Thanks to Vladimir Botka, i got some inspiration from his answer.

Its been resolved using the script below.

Parent Script : test_dummy_sw_fw.yml

- hosts: localhost
  become: no
  gather_facts: no

  vars_prompt:
    - name: username
      prompt: "Enter Username (Local/TACACS)"
      private: no
    - name: password
      prompt: "Enter Password"
      private: yes

  tasks:
  
  - set_fact:
        ansible_user: "{{ username }}"
        ansible_password: "{{ password }}"

# Test Script on Switch

- name: Execute Script on Switch
  import_playbook: test_dummy_switch.yml
    
# Test Script on Firewall

- name: Execute Script on Firewall
  import_playbook: test_dummy_fw.yml

Child 1 / Switch : test_dummy_sw.yml

- hosts: localhost
  become: no
  gather_facts: no

  pre_tasks:

    - when: ansible_user is undefined
      block:
        - pause:
            prompt: Enter Username (Local/TACACS)
          register: username
        - set_fact: ansible_user="{{ username.user_input }}"

    - when: ansible_password is undefined
      block:
        - pause:
            prompt: Enter Password
            echo: false
          register: password
        - set_fact: ansible_password="{{password.user_input }}"
    
- hosts: Switch
  become: no
  gather_facts: no

  tasks:
    - set_fact: 
        ansible_user: "{{ hostvars['localhost']['ansible_user'] }}"
        ansible_password: "{{ hostvars['localhost']['ansible_password'] }}"
    
    - name: Interface up/down - SDL1
      ios_config:
        lines:
          - description Testing Switch
        parents: "interface Gi0/0"    
      register: print_output
      
    - debug: var=print_output

 

Child 2 / Firewall : test_dummy_fw.yml

- hosts: localhost
  become: no
  gather_facts: no

  pre_tasks:

    - when: ansible_user is undefined
      block:
        - pause:
            prompt: Enter Username (Local/TACACS)
          register: username
        - set_fact: ansible_user="{{ username.user_input }}"

    - when: ansible_password is undefined
      block:
        - pause:
            prompt: Enter Password
            echo: false
          register: password
        - set_fact: ansible_password="{{password.user_input }}"

- hosts: Firewall
  become: no
  gather_facts: no
  
  vars_files:
    - if_dummy_asa.yml

  tasks:
    - set_fact: 
        ansible_user: "{{ hostvars['localhost']['ansible_user'] }}"
        ansible_password: "{{ hostvars['localhost']['ansible_password'] }}"

    - name: Interface Config on Firewall
      asa_config:
        lines:
          - description Testing Firewall
        parents: "interface Ethernet1"  
      register: print_output

    - debug: var=print_output

When we executed the Ansible script on parents it will only prompt the credentials once because the credentials has been set previously on Parent Script, so prompt will be ignored on child script.

When we executed directly on child there will be a prompt since the credentials of ansible_user and ansible_password is not defined on parents.