From a baby’s birth, begin creating a secret pictorial keepsake for the future.
Create an email account that is password-protected, where you can document stages of the child’s life. Simply email photos to that email address to document the occasions.
On his or her 16th birthday, give that young person the email address and password that will show them all the photos you’ve taken, each one documented with the date and time. Quite a keepsake.