Day trips, a castle, rock pooling, crabbing at the harbour with a bucket and a bit of bacon. There is a nature scavenger hunt for the days you cannot face going far, and a no screens day for the days when everyone has clearly had enough of them.
Camping overnight is on there too, which either goes very well or becomes a story you tell for years.
Fifteen ideas.
Free, nothing to sign up for, and there is one for every month if you would like the rest.

