However today's conventional wisdom is that a child should never carry over 1/5th their body weight. (Man, we totally coddle them nowadays, don't we?) So for 12-20 lb load a heavy duty daypack works (ie one with a hipbelt).
http://www.rei.com/REI-Outlet/product/768911Time to trade in that Coleman white gas stove for a pop-can alchohol stove and the iron dutch-oven for a Titanium cup and use
freezerbag cooking.