When my kids were small and funds were very limited we used to.
go to national trust places. I would spend my February council tax free month money on buying annual national trust membership and use that for numerous days out throughout the year. We are lucky that we have lot of places near by.
do the library summer reading challenge.
meet with friends at the park.
we were lucky to have an open air local pool which I was an opener for so the kids could go to for free - I know this isn’t an option for most.
go on bike rides
go to the beach - one with no facilities so no spending and take a picnic.
Arts and crafts, den making at home, baking.
make dens in the woods.
duck races if you have rubber ducks and a local stream.
Make the most of the councils summer free play days. I don’t know if these are still a thing.
visit family
wild swim in the local river
have a wander around the local animal rescue place. Often they’ll let the kids help clean out the small
pets etc.
there’s lots that can be done. But it does depend where you live.