I haven’t read the whole thread so apologies if I repeat something that another poster has suggested.
I do feel so sorry for you all as the UK isn’t used to any sun at all really, which is why the British are mocked for allegedly only talking about the weather!
In most of Africa, southern states of USA, South America, Indonesia, India, Australia etc., etc., it is very normal to have 30+ or even 40+ weather.
I don’t have aircon - I have fans and shutters. My children have coped with going to school in 40+ degree heat and the blinds are closed and the ceiling fans are on. We have winter where it’s below 10 overnight and in the low twenties in the afternoon, then the temp drops quickly when the sun goes down.
Make sure that your kids know how to apply sunscreen, especially to ears and noses and have wide brimmed hats.
Try to get them in the thinking that having a cup of water per hour is normal. A child size cup!
If at all possible, get lightweight long sleeved cotton tops for them to wear. Clothes offer* *some protection against the sun but not much, about SPF 10 but every little bit helps.
Keep curtains drawn during the day and windows closed, open at night, after dark to take some of the heat out of house, which I know is quite late as you have the long evenings but unfortunately you’ll have too, just to relieve the heat inside.
Keep meals plain and simple, tuna mayo with salad, precooked supermarket meat with salad, beans on toast. Try not to cook as you will just heat the house up more, especially slow cookers which can act like a radiator.
Enjoy how white your whites will get after being in the sun and hang anything not white in the shade so it doesn’t lose it’s colour.
Be creative with hairstyles, now is not the time for hairdryers, curling tongs or straighteners.
Try not to use appliances that give out heat such as vacuum cleaners, except either early in the morning when it’s cooler or late at night as it’s cooling down.
Definitely use the oven, iron or anything else. People who live in hot countries or places soon realise that if you wash clothes, shake them out and hang them up to dry, they don’t really need ironing!
Do not let your children out between 10.30 and 4.30 as the heat soon builds up. I know it’s tempting to get a paddling pool and stick them in it, but unless they are wearing SPF50 wetsuits, they can and will burn and also get sick with either heatstroke or something equally awful. I’m not sure if you can buy SPF clothing in the UK, can you?
And remember, for you lot in the UK, it’s just days or a few weeks of heat. Some people have it for months and don’t have aircon or can’t afford to run their aircon and they manage!