Children would all need to be provided with the appropriate clothing - that would be hiking/ski gear type stuff. That would be expensive and many families wouldn't be able to afford it.
This comes up time and again on here, and it really isn’t true. It really isn’t that expensive if you shop in supermarkets, H&M and secondhand. You don’t need a North Face coat and Burton ski pants. It’s a question of prioritising decent, warm waterproof clothing over useless fashion items.
Have just double-checked, and you can get a pack of three pairs of magic gloves for £4, or if your child feels the cold, proper Thinsulate ski gloves from £5 (Sainsbury’s). Fleece-lined hat with ear flaps from H&M for £4. DS’s waterproof trousers came form H&M and were £9, or Mountain Warehouse have some for £13. I am assuming most kids have a coat and wellies already, but if not wellies are about £10 from any supermarket, and a good waterproof coat (H&M or M&S) is about £30. So if buying all new, £60, which the majority of two-income households could probably afford, assuming you get two year’s wear out of most of that and would have been buying a coat and wellies anyway.
If you are buying secondhand, there are Jojo waterproof salopettes on FB for £3, and good, branded waterproof coats for £8. Wellies from £2. So you could get everything you need for under £20. Again, the vast majority of families can afford that, and would have budgeted for a coat and wellies regardless. There are children who don’t own a coat, but I live in a very deprived area myself and the vast majority of primary kids do in fact have coats on in a morning.
The school should definitely have a stock of spares for those who don’t have them, but most families in work should be able to find £20 every couple of years.