Kids are adults now, but 10 -15 years ago we would
Free or almost free
have friends round to play for the day - probably do make your own pizza for lunch, and do some baking buns and icing them. Would hope for a return invitation later in the week or for another holiday.
Park - walk, playground equipment, feed ducks, take a picnic but buy a hot choc or chips from the cafe.
We live in a city so several free museums/art galleries.
Geocaching. Again take a picnic/snacks and treats.
Each child choose a meal, - cost, buy and cook with help where necessary. Not free but we need to eat.
Board games/Lego/jigsaws.
Local National Trust gardens and playground - we are members and take a picnic.
Cost a bit - would probably only do one of these in a half term holiday
Cinema trip - when a bit older double up with friends so you don't pay for adults to go - you can sit in the cinema cafe with the other mum or dad with a coffee while the kids enjoy a film or once secondary school can just go with a mate.
Bowling - again if you go with another family you can just pay for the kids to play - take your own snacks or set expectations for only one drink each.
Swimming - again would go with another family so you only pay for your kids and the adults stay out of the pool (probably can only do this once kids 8+ and can swim).
Once a bit older - mooch round IKEA and lunch in the cafe. My kids adored this, and frankly still do!!
Cost more: maybe one of these
Takeaway and film night.
Paid for museum.
Farm park/soft play with lunch.
Family meal out eg Pizza Express on Tesco vouchers.