Most children of school age who wet the bed at night have what doctors term primary enuresis.. They have never had nighttime control of their bladder. Family history plays a role, too, in incontinence in children. If you wet the bed as a child, don't be surprised when your child does, too.
One thing to notice is that if you put a gallon of air on a scale, (in a wieghtless container, of course) you would measure zero, exactly. That's because the buoyancy caused by the surrounding air exactly counteracts the weight of the air in the container. If you pressurized the air in your gallon container to, say ten times the outside pressure (or 147.0 psi absolute, or 132.3 psi gauge) it would now weigh nine times 0.01, or 0.09 lb.
The air inside of the balloon has weight too. A cubic foot of air weighs .078125 pounds. A medium size balloon will hold 90,000 cubic feet of air and suddenly you have 7,031 pounds of air mass to contend with. This mass does not include such things as the aerodynamic load on the balloon, the weight of the balloon system itself, or the passengers and crew.