Just because it will be boring for you isn't a reason to cancel (since it's more about your son having fun than you having fun anyway).
But the temperature is a definite concern, especially for those who haven't camped before. 40-50 degrees during the day isn't a big deal, since you can just pack extra warm clothes, gloves, and jackets. But for the 20 degree night, you will need more than just one sleeping bag each (unless they are the super-expensive, negative 20 degree rated or better type). A beanie for your head at night is also suggested, since you can lose a lot of heat from your head when it 20 degrees. A 20 degree above zero rated bag will NOT be warm enough... it just means you won't die or get hypo-thermia if it's 20 degrees... but you will be miserable. You will also want extra insulating layers under you, and no, air mattresses don't count as insulation... just padding. So, whether you use an air mattress or not, you should also have an extra comforter, sleeping bag, or foam pad beneath you so the cold isn't sucked right out of you (therma-rest type pads, though, are great insulators).
Have I gotten across how bad the cold can be at night? If you go you'll be fine, AS LONG AS you bring really good sleeping bags, or mediocre sleeping bags and a whole bunch of extra comforters and blankets. Oh yeah, wear sweat pants and socks to bed so that when you have to get out to pee at night, you're already dressed.
But don't baby your son. This will be a great experience for him, as long as you bring him the proper gear, tell him how to use it, and then let him be. He'll be tougher and learn faster if he doesn't listen to you and freezes his butt off all night. Trust me, he won't do it again, and next time he'll know).
If you are this concerned, you should really call his scout leader and ask more questions about what the trip is like. But it would be great for your boy.