They definitely should not be allowed to run loose on the floor fot they might be inadvertently stepped on or quickly disappear behind a piece of furniture or an appliance, and be difficult to recover. Plastic balls which allow hamsters to run all around without really being loose are excellent exercise options. Hamsters should never be allowed in the vicinity of dogs or cats. One swift bite or swipe of a claw could be the end of the hamster. Hamsters make ideal pets for children, and can be the perfect critter to introduce them to the joys and responsibilities of pet-care.
Kids are prone to drop or otherwise injure small animals.
Be very alert to possible disasters when children and small animals mix. Unfortunately, hamsters do not live very long. A three-year old hamster is a rarity. The normal life span is about two and a half years, though many pet hamsters don't make it that long because of poor pet husbandry practices. Perhaps the biggest threat to every pet hamster is keeper negligence.