Every meaningful action is appended to your family record: messages, events, expenses, handoffs, check-ins, calls, who joined and when.
Each entry is fingerprinted together with the one before it, forming a chain. Change any entry and every fingerprint after it stops matching. The database refuses updates and deletions outright, so this isn't a promise the app makes — it's something the storage won't allow.
Anchoring
Once a day the end of the chain is timestamped by an independent time-stamping authority. That's what lets you show that an entry existed on a given date and hasn't changed since — without asking anyone to take our word for it.