@ Ze’ev Ionis
This is probably more common “older” families rather than “younger” one. My children 3 and 6 have email address that I maintain. They’re practically required anymore because it seems all child sites require an account.
What I think you should do, is add a single entry (not a family) that they will maintain. Nearly all families share the same last name. For the first name, you could simply add both spouses first names. As an an example “John & Jane”.