The offline photos idea would be a wise choice until the child has grown up and can make the decision but let us assume your wife will not accept that approach.

The Proton Drive idea also sounds reasonable since you already use that service. You should password protect the shared link but you will want another communication path than email to share the password to your shared folder. Use different folders with limited expiration dates (3 months?) for different sets of photos. Be sure to write to relatives that they are not to share the photos. We get emails asking us not to share things, be it links to photos or sensitive topics such as health. If someone breaks the rule, you may have to “ground” that person by cutting off their access to folder sharing for a period of time. You must communicate the “grounding” to others but that person might still go behind your back and get the link and password from a sympathetic someone else.

Have you thought about using a Fediverse instance for family and friends? There is a fantastic blog post on this subject. https://runyourown.social/ You would end up running a fork like Hometown that allows you to keep a portion of your community not federated where family and friends can share pictures with each other so that only users with accounts (plus your web server staff) can access your photos. https://github.com/hometown-fork/hometown You would be helping out many family members and friends instead of only helping your child. You would get more family and friends to support you because they would also be invested in making your Hometown server work for them. Find a relatively safe web server to host your data. https://www.eucloud.tech/en/eu-providers/vps-hosting