Young children do not know the dangerous of this toy, they might consume it or swallow it. Young children if swallow this toy, it will expands in their stomach as fluids that make it expand and children will die because of this.
Some parents might not know of this that young children or toddler will take this to put in their mouth. As you know young children likes to put anything in their mouth. It's important to be aware of what's happening and always keep an eye on our children.
Just something to share with everyone, don't leave your children alone with this toy.
If you are insist on playing the expandable toys, get a empty bottle that you can sealed it after putting in the expandable toy and water. That's what I usually do, in fact we have this freebie expandable toy from local snacks food. It was a dinosaur expandable toy.