Do both parents need to register?

Since Waldo allows for sharing a matched photo stream with up to 6 family members, only 1 person should sign up. Once you've signed up, open the Waldo Photos app and tap on the album you wish to share.  Then tap the icon that says "stream" and follow the prompts to choose from your contacts and send out the invites. Those you've invited will be notified via text and will follow the link in that text to download the Waldo Photos app and accept the invite. (They should not be prompted for a Join Code or payment, if this happens ask them to delete the app, go back to the link in the text and try again.)