Does this exist? A decent sleeping bag for my boys, 9 and 12, that is classed as 3 season ie, would have been okay last night in a tent. Their current ones are rubbish, needed onesies and hoodies.
The other thing- needs to be cheap ish.

Yes. Get to Decathlon, good and well priced.

I had a snugpak softie as a kid…. http://www.snugpak.com/ great bags and fairly cheep…. lasted me about 10 years of scouting and is still in service for an indoor bag….
Edit. .. just looked and they are a bit pricey nowdays…. still good tho.

What about trying a cotton liner bag in the bags you already have? They make quite a difference.

They won’t be 9 & 12 forever so get them a decent adult bag. Snugpak, Vango and Decathlon are usually very good value for money. Sadly with sleeping bags really cheap usually means really crap.
Have a look for sales at online outdoor shops. Bags from Marmot and Mountain Hardware sometimes comes up in the sales. Mountain equipment are also very good quality and not too expensive.

I’m not a camping expert by any means, strictly fair weather for us, but when it is cold I find keeping them in their normal pyjamas and letting the bag do the insulating works a lot better than wrapping them up inside the bag. A blanket over the top of the sleeping bags keeps them toasty (I have a few of the mesh type ones they use in ambulances)

You could always try, and I know it’s a bit extreme, an extra blanket or two.

I believe the correct way to express the level of exasperation I feel is FFS….

Vango Nitestar is the bag of choice for smaller people, but we’re talking quite small children here. At 9 & 12 they are into youths sizes, not sure if Vango do bigger versions of the Nitestar.

Decathlon look good.
Do the liners get all twisted up though?

Crikey, yes, that is an option, but an extra blanket would not do, more like a duvet, with blankets underneath. We don’t have the room to pack that much extra.
My old vango was fine with no extras, but I spent the night worried about them , in their shit sleeping bags.

If they wiggle around the liner moves with you

Top tip: a hot meal shortly before bed time helps an awful lot.
Synthetic and down insulation work the same way in that you heat it then it keeps you warm, so if your body is busy digesting food it’s generating warmth.

Another thing to remember is that your sleeping mat can be critical. You’ll lose downwards too. A decent mat will stop you losing heat to the ground. Opinions vary on the best way to do this but again good mats are not cheap but worth it if you get a good night’s sleep

self inflating mats instead of airbeds will be warmer.

We have some Blacks ones that the kids are starting to outgrow at nearly 5′ (10 & 11 year old). They are ace, and are just about a 3-season. Add a fleece blanket and good PJ’s and they are snug and warm.

Another one here for Vango Nitestars . I have the standard 350 and my wife and daughter have the 350 short.My daughter has had one for the past 6 years, since she was 7 and still fits with plenty of room to spare. Bag is still very warm as we found out last weekend when it was down at 3 deg during the night. We use a fleece liner as it helps protect the bag and gives a little extra insulation.