It is to give the parents 30 minutes or so at the picnic before they have to go back to keeping an eye on the kids in the water.
I never thought of that, but there’s probably some truth to it. Maybe it’s the same with parents telling their kids not to sit too close to the TV or it will ruin their eyes, when in fact, it was a ploy to keep their heads from blocking the TV screen.
In m case, just enough time to help my mom do the lunchtime dishes before heading to the swimming pool.