As ripcord (above) stated, mercurialism (mercury poisoning) can be fatal, especially for children, as they are susceptible to poisons in smaller doses that most adults.
Acute (short term) mercury poisoning, as with many other forms of heavy metal poisoning, causes nausea, vomiting, abdominal pain, bloody stool, severe kidney damage, renal failure and death. Chronic (long term) mercurialism causes, oral inflammation, muscular tremors, personality changes, irritability, blindness, dysarthria (slurred speech), dysphagia (difficulty swallowing), deafness, spasticity, tunnel vision, pendular ataxia (wild arm & leg movements), general malaise, fatigue, toxic encephalopathy, neuropathy, coma, stupor, intellectual impairment, central nervous system failure, death and a whole host of unfavorable symptoms. These symptoms are not always reversible and children tend to have a low recovery rate.
Mercurialism is caused by the oral ingestion of mercury, inhalation of vaporized mercury, as well as improperly handling liquid mercury. Mercury is readily absorbed into skin, hair, and clothing. So, if a mercury thermometer breaks, DO NOT allow children to play with the mercury.
Not very long ago, we were not as well aware of the effects of mercury on the human body which is likely why Anne2 (above) was allowed to play with mercury as a child and handle it as an adult without proper protective equipment.
If a mercury thermometer breaks:
Wear gloves and avoid contact with bare skin.
Block off the spill to prevent spreading, remove unaffected parties, block drains & cracks, turn off AC or heater, close all doors to other rooms, open all windows/doors to the outside.
Sweep the mercury beads together with a playing card or stiff piece of paper into a plastic dust pan or use an aspirator to pick up the individual balls.
Work from the outside of the spill area toward the center. Work over a plastic tray when putting mercury and contaminated items into the bag/container.
Use a flashlight to look all around the area of the spill. Since mercury is reflective it'll be easier to the flashes of light bouncing off of the balls.
Sprinkle sulfur powder area of the spill after cleaning; the area will turn yellow or brown if mercury is still present and the area needs more cleanup.
Sprinkle zinc flakes or copper flakes to clump together any small amounts of mercury remaining.
Collect all mercury and ALL contaminated items, including clothing and shoes, into a zip-lock bag or other leak-proof plastic bag or sealable tupperware.
Shampoo and shower after the cleanup.
Take the bag or container to take to a mercury recycling center.
*Note:All supplies can be found at a hardware store.*
If the spill is larger than the size of a quarter (more than one thermometer would have to break), block off the spill to prevent spreading, remove unaffected parties, block drains & cracks, turn off AC or heater, close all doors to other rooms, open all windows/doors to the outside. Leave the area and immediately call the local health department and your State environmental protection agency.
Hint:
If you prefer the accuracy of a glass thermometer over a digital one, you can use an alcohol thermometer to further minimize risk to you and your children if it should break.