Pads--can you sleep on a CCF (closed cell foam) pad? If not, can your son sleep on one (my 13-year-old grandson does). If so, you can get them for $15-$30 each. Be sure to test sleeping pads in the store and again at home, where you should spend at least one night, maybe two, on the floor, while you can still return them. Your first night on the trail (when it's hard to sleep anyway) is not the time to find out your sleeping system is uncomfortable!
At least check for EN13537 ratings on the sleeping bags. If none, add 10-15*F to the manufacturers' ratings. Also, watch the girth issue--the bag needs to fit over all your insulating clothing without compressing the insulation (you may need that for extra cold nights). Finally, compare weights; if you have to go synthetic, some synthetic insulation is warmer for its weight than others.
Please keep us informed how your son is doing. We care!
May your trails be crooked, winding, lonesome, dangerous, leading to the most amazing view--E. Abbey