OP, my partner is a teacher, I'm also in a professional job (albeit working PT). We can't afford to do anything either.
I've got two at 11 and 8, he has one who is 7. We have had one day out at a farm this Easter. That was £45 plus picnic cost. That includes the fact one adult was free as a carer.
I'm taking my 2 DS to a museum tomorrow as we can't afford to do any paid activities. Even that costs though as we will need picnic things, plus either pay for the train or parking/fuel. Yes, I am counting every penny right now.
Other things I've found to keep them entertained in the lower end of costs:
Swimming near us in the council pool is £15 (but we get a free carer in that) Seems expensive for an hours entertainment if I'm honest though! Plus all the washing after and everyone needing a shower to wash hair because the pool showers don't stay on without you holding them down and are like piss dribbling out. Water, electric and gas costs bump that up by at least a fiver! If you've got decent showers though, I'd probably be more inclined to go!
Reel cinema is £3.99 before 1pm. You may have one of these near you? Or the juniors showings at various cinemas in the mornings for the 8 year old - they are £2-3 usually.
Tenpin (that's the name of it) bowling is £3 per person for a game locally to us. So for 5 of us 2 games is £30 which is half the cost of the local Hollywood Bowl.
We do have a national trust membership, and again we are lucky that for £30 a year it covers all 5 of us as we get 2 essential carers for free. However we seem to live in a bit of a black hole with not many local NT places. We tend to use it more when visiting family in other areas.
Without the carer discounts, we'd be even worse. Mind you, if I wasn't caring for my son then I'd be able to work full time and have an extra 1k a month. So I guess it is swings and roundabouts.
All I know is I'm fed up. I'm penny pinching everywhere. We don't eat out at all now. Not even McDonalds as that is expensive, creeping up to £4 for a bloody happy meal! I'm utilising discounts wherever I can (blue light card, DS works at a supermarket so I always use the staff discount card etc). But it just doesn't stretch to fun. We used to do something every weekend, even if that was just soft play with some lunch there. Hell would freeze over now before I'd pay £50-60 for that now! I try not to dwell on it as if I'm honest it makes me feel really down and like there is little joy in life anymore. What was the point in us both going to uni and working hard? We even get universal credit ffs! We should be able to afford to live a decent life without benefit top ups!