Allowing a contact to update their related contacts via Webform-CiviCRM
If you have the Spouse and the Child set up with Relationships - and you configure the webform to have 3 contacts, and you set the contact 2 "Existing contact" webform component to have a 'default value' based on 'relationship to contact 1' then I would expect that using a checksum for contact 1 should result in those other contacts being prefilled. Is that what you need?