You can issue a certificate for multi-children families’ status from the Supreme Confederation of Multi-child Parents of Greece (ASPE).
Requirements:

• you must be a member of an Association of Multi-child Parents - Member of the ASPE 
• your Multi-child Parents identity card (booklet) must be valid. In the case of a child who does not have a Multi-child Parents identity card, the Multi-child Parents identity card of at least one parent must be valid.

You will need to:

• fill in your personal Taxisnet credentials
• attach the necessary supporting documents (a certificate of marital status and a photocopy of both sides of your identity card bearing your photograph and the validation of your identity card respectively)

The certificate is not issued immediately (online). When the certificate is completed, it will be sent to the citizen's inbox and you will be notified by e-mail and text message (sms).

The certificate, which has the security features of gov.gr, can either be sent electronically or printed and submitted in hard copy. The paper version does not need to be validated and is confirmed by the gov.gr document validity application.

If it is not possible to issue the certificate electronically, you should apply to the Association of Multi-child Parents - Member of the ASPE of which you are a member.