Whats the best strategy for keeping kids safe online?

My plan right now:
1. Start with a dumb phone (only call/text) once a phone is "needed".
2. Switch to a smartphone with Truple once I feel my child is mature enough to safely manage a device with parental oversight via Truple
3. They leave the house and are on their own, but hopefully the time in the house with Truple allowed me to coach them to reaponsible internet use.