Sunny 16 at the beach needs adjusting. The sand is an excellent reflector and you have a lot more light coming from below than with a subject on grass. Sunny 16 minus one stop would be better.
sunny 16 doesn't need adjustment at the beach since it's starting point is for seashore and snow: f16 1/125 for iso100
This was shot using Av mode before I knew of things such as Sunny 16. Exposure compensation was set to zero and I used evaluative metering. I picked f/8 and 100 ISO and the camera picked a shutter speed of 1/800. That exposure is equivalent to Sunny 16 minus 1 stop. This has had no edits and I think the exposure looks a tiny bit dark, but very useable. That said, it can take another 1/2 stop added to the exposure in Lightroom without blowing anything (even the white teeshirt) or looking overexposed.
IMHO your first photo there is under exposed by about 1 stop, and it isn't just a "tiny bit dark". So again sunny 16 at the beach would have been the right call to use since you under exposed it by about 1 stop.