Seagull Beach is my favorite "big beach" that's nearby. Our parking sticker for town beaches gets us in for free, which is an added benefit. I took the boys there on a weekday afternoon while Peter was working and we had a fun time. They got along well and didn't fight--it was a miracle!
We tried to go back to Seagull Beach on a Saturday a couple of weeks later, but they weren't letting anyone else in because of capacity limits--COVID strikes again! But at least we got in one good day there this summer.