With kids, give Duomo 'Secret Terraces' / Rooftop Tour a miss.
A guide takes you onto galleries and terraces closed to general ticket-holders, getting you eye-level with the dome and the marble façade's detail — a quieter, more intimate angle than the standard climb. The catch: it's a premium add-on with limited slots, still involves stairs, and overlaps with what the regular dome ticket already covers for many people. Worth it mainly for the dome-obsessed who want the deep version.