Wasps trying to get in sandpit

[DrKnowNothing]

OK so just bought a sandpit. We are being plagued by wasps trying to get into it, so much so I've dumped the sand on the lawn and filled the table with water instead.

Is it just us? What do they want, and can I persuade them to go away?

They nest in the ground in late summer (prep for overwintering), although I'm surprised at a sandpit choice because it's too loose material; they prefer harder sand.

Ragged, it's one of those ones that is half 'dry' for sand and half wet. It didn't take long for both sides to be wet, we then drained the excess water so we probably made the ideal habitat for them. I know better to keep it dry next time, shame DS will have other ideas ;)