The concept is simple: create a small, personalized helium balloon type device designed for persons aproximately 25 pounds or less, to function like a floating stroller.
The child would be placed in a secure and comfortable harness type seat, with holes for the legs, like in those baby walkers we've
seen for years. With a safety line attached to the front of the child's seat, one would proceed to fill the balloon shaped floater with helium gas. Models could be equiped with a gauge showing pounds of lift, so that parents could easily match the weight on the gauge to the child's weight.
Once the balloon has achieved liftage equal to the child's weight, the child essentially becomes weightless and can be elevated by hand to a safe distance above the ground where he will neither sink nor continue to rise as his weight is exactly counterbalanced by the the helium balloon.
The important thing to keep in mind is that this product must only be used by safe and competent adults, and most importantly, that the safety line MUST be attached at all times to avoids dangerous mishaps such as mischievious siblings deciding to play volleyball with little brother at the family picnic, launching him into orbit, or sending him off to hover over the lake at an altitute of 75 feet. Or perhpas a simple gust of wind could carry a little girl many feet up, and yards or even miles down the way. It could be hours before she is discovered by a cropduster, as she nonchalantly hovers over a random cornfield.
I agree this idea does not come without risks, but think how easy Disneyland would be? Or the beach - no fear of the young one running off, or worse - drowning - while he is happily floating four feet off the ground and secured to the picnic table. How about the supermarket - simply foat the youngster out of reach of all those tempting items they assuredly grab for while you are making your selections!