We measured UV penetration under both setups using a calibrated meter. The results surprised us.
Test Setup
UV meter at chest height (where kids sit), 4 hours of midday sun, identical beach position. Three runs averaged.
Results
Beach umbrella (7ft, UPF 50+ rated): UV index 2-4 inside (varies with sun angle)
Beach tent (4-person pop-up): UV index 0-1 inside
Why the Tent Wins
Umbrellas block direct sun, but reflect off sand/water. Tents have 4 walls + roof = enclosed UPF 50+ zone.
For kids under 5: Tent. Non-negotiable.