Site selection is quite important. Stay out of creek bottoms and places where cold (heavy) air will settle. That is easily worth about 5-10F right there.

Do not sleep on cots. Get down on the ground and insulate, as others have noted, with two or so pads (not air mattresses!).

I like to wear a warm base layer inside the bag,with something that covers my head and the large blood vessels in the neck.

Have a bit to eat before retiring. Chocolate is great for this purpose.

I wonder if your sleeping bags were honestly rated. Believe it or not, some manufacturers will exaggerate. 20F isn't really all that cold.

I second hikermor's suggestion to choose your site well.

I always use at least two sleeping pads, one closed cell-Thermarest and a cheapo blue pad, along with a mylar blanket underneath and a wool blanket to go over my cold weather sleeping bag, I'm usually toasty warm.

We eat a hot, high fat snack right before bed too, to get the internal furnace going. bacpacboy particularly recommends a hot chocolate and hot dog and/or cookies/smores. This mama likes a shot of kaluha in hers. A wool watch cap and socks, along with good old johns, always serve me well, even with an arthriticy hip.

Not sure about your troop tents, but ours were too big for a long time, for winter camping. Bigger, higher domed tents allow the youth lots of room, and tend to be more budget friendly, but makes for a lot of dead air space, which I find makes it cooler than in a smaller tent. Our group has upgraded to smaller Eureka tents now, and get fewer complaints about sleeping cold. (Let's face it, someone's always going to complain.)

A vapor proof lining -- also called vapor barrier -- inside your sleeping bag has its use, but for most of us it's purely theorethcial. The vapor barrier prevents condensations to accumulate inside the insulation of the sleeping bag. You loose a cup or so of vapor through sweathing each night, and if all of that accumulates for days and weeks then the insulation value gradually drops. Essentially, you get lumps of ice inside all that nice fluffy insulation material. Not good.

Most of us aren't at polar expedititions that lasts weeks, and would rather not deal with the downsides of a vapor barrier: It gets rather clammy and damp.

If your sleeping bag isn't up to it, I've had great success making lining out of army surplus wool blankets. Fould doble and stitch a cocoon with an inch or two wide stitches, it takes 2 minutes, cut away the surplus. Heavy, bulky, but works wonders to augment a sleeping bag.

I haven't tested any of the fleece liners, but I'm sure they're good.

And wool underwear. I'm a big wool fanatic. Modern merino wool is fantastic.

Oh, and like several other has mentioned, good insulation to the ground is important. Your sleeping bag will squeese flat under you, and not provide much of insulation. In winter, I too use two cell foam mats or one cell foam + one of those wonderful "exped downmats". (The exped downmat in itself provides plenty of insulation and wonderful comfort, but I want backup in case of a leak.)

The dynamics of your discomfort-warm enough initially, foot discomfort later-suggest that nutrition/and hydration issues may predominate. Your feet are at the end of the circulatory line, and tend to be the first place that shortage of fuel and fluid show up. Winter camping requires high quality, purpose-designed equipment, or a very old-fashioned approach. A tiny snow-cave, lean-to or pup tent may be more comfortable than a large and airy 3-season tent, wool blankets and woolen clothing may prove superior to multiple layers of summer-weight synthetics. Whelen and Baker tents are designed for cold weather use in combination with a fire, and the kifaru folks have amazingly light tents and tent stoves. A tepee, yurt, or cave will accommodate a lot of campers and a fire for cold weather applications. Folks have been living rough in the cold for thousands of years, and the technology is there to make it a comfortable experience: but it is the not the technology of synthetic, ultra-light, inexpensive big box retail outlets that does so.

don't sleep in your day clothes they well be too damp even if you can't feel it.a total change into dry sleeping gear is hard because your putting in cold clothes.it's tempting to get into the bag in body warmed up stuff but the damp will chill you and the bag will get damp as your body uses calories to dry the clothes you wore all day.
i would suggest striping down and putting on a polyfluff sweat suit and polyfluff soxs and hat.
a bit of a snack before bed helps but stay away from drinks or you will find trying to pee in a bottle or zip lock in a sleeping bag is a looser.

wildman, I'll have to check those out.

teslinhiker, looks like some good tips there, but I do have to be careful about eating too much before bed as I am diabetic, and we have a boy in the troop with a horribly bad peanut allergy so can't go that route either. Also, we did use a fleece sleeping bag liner, it helped some but apparently not enough.

denis, thanks for the input, adding to my list of possible things we can do better for our next outing

hikermor, yikes no cots? I'm wondering why as it seems to me like I sleep warmer on the cot than on the ground? But then, our sleep pads are not the best, I'll have to look into all the sleep pads that have been recommended here.

hikermor and BPJ, as far as site selection, we didn't have much choice in that matter, it was a council run event, we were on top of a mountain, a reclaimed strip mine site, no trees or shelter to speak of, and we had a designated camp site. The size of the tent may have also been an issue, as they were tall enough for me to stand in and i am over 6 ft.

mostlyharmless, I will have to see if i can get my hands on some wool blankets for that purpose, and as everyone else has mentioned better insulated padding for underneath

nursemike, I suppose that is a possibility, although we stopped to eat before we went to the camp site, a pizza buffet, figure there was plenty of fat in that meal, and as i recall we ate hot cups of noodles before going to bed, not the high fat snack everyone has been mentioning, but it was good and hot. Another factor, at least for me, is the complications of being diabetic for nearly 40 years compromising (at least to some extent) the circulation in my feet. The hydration could have been an issue, especially for my son as he tends to not want to drink enough for some reason (probably because I am always onto him about it and he is 13 and knows everything so dad is automatically wrong). My feet were certainly chilly, but I think I would have been fine til morning if my son hadn't come to my tent complaining of his feet being "numb" (in hindsight, they were most likely just very cold and he noticed it when he was putting his shoes on for a trip to the bathroom). The tent was also far less than ideal, but we had done ok in them at previous camp outs with similar temps (the drop to 15 degrees was VERY unexpected). It was also all we had to work with as far as the troop equipment goes, although I might have brought a smaller tent from home (7 by 7 ft footprint).

canoedogs, that is good advice. I can't say for sure that my son did, but i know i changed out of ALL my clothes and into dry underwear, long johns, and a fleece top and flannel bottoms. the down side of this was, I got very cold right before getting into the sleeping bag, which is not supposed to be a good idea is it? How does one make the change into dry clothing without getting cold outside the bag or compromising the bag with damp clothing (i.e. climbing into the bag to change clothes)?

A big thanks to everyone, I hope all this info will make for a better (and warmer) cold weather camping experience for my son and I next time around.

12 Person Cold Climate Tent With Bunk Beds
A complete systtem that consist of a genuine military surplus Olive tent with fiber fleece lining, windows and heater pipe vent exit port. This tent comes with 12 bunk beds, all poles, stakes and accessories: at major surplus
Admittedly, a little pricy at $2495 and heavy at 480 pounds, but it's fleece lined!

Reclaimed strip mines may not make the best campgrounds. I much prefer spending time in areas (e.g., Gila Wilderness) where one is free to camp wherever.

I agree that a smaller volume tent would be more satisfactory - lighter,more wind resistant, and warmer due to less volume.

Two CCF pads will give plenty of insulation.

I have several Wiggy's bags, and so far I've never slept cold in one of them. I have two that are designed to "nest" together into one bag, and in that configuration it's rated for -40 F. Ratings are sometimes pulled out of the air and there's no objective way to test them but Wiggy's seem to be rated pretty fairly. If it's really cold I might also wear my Wiggy's Sun Walker booties in the bag, too.