I would be really worried about these for young children. Actually, even fool hardy teens.
They have the potential to be really dangerous or even fatal. It is not something I would ever allow children to use without close supervision.
Maybe we are talking about different things? I can't see how a child who knows not to eat plastic could harm him/herself with these. It is essentially a sheet (probably A5 size) which has several layers - plastic on top and bottom, and a gel polymer in the middle. You hydrate the polymer in water, and either freeze for cold applications, or heat in the microwave for hot applications. Nothing leaks out or can be accessed without knives and scissors, and you can cut the sheets to the size you need - be it individual cubes or smaller sheets. They are reusable and dry, and do not melt (hence the name dry ice) but do not contain liquid nitrogen. This
is what I am talking about.