These disc batteries can be access by small children if they smash apart the toy. The Consumer Products Safety Commission says two kids have had problems with batteries; one swallowed it and the other stuck it up his nose.
The danger is that when a disc battery is inserted into a nose (for example), a localized electric current is created between the positive and negative poles of the battery within the nose. This electric current basically "electrocutes" the lining inside the nose leading to tissue damage and ultimately necrosis (tissue death) within an hour. The same applies even if the battery is swallowed or put into the ear canal.
Treatment is IMMEDIATE removal... as soon as possible. Regardless of the day or time. STAT...
In the last 10 years, 13 deaths related to swallowed batteries have been reported, 12 of which are due to disc batteries (20 millimeter lithium cells).
Small children should NEVER be able to access disc batteries.
Read the NPR story here.
Read about the recall itself here (also from NPR).
Preventing Battery Ingestions: An Analysis of 8648 Cases Published online May 24, 2010
A Review of Esophageal Disc Battery Ingestions and a Protocol for Management Arch Otolaryngol Head Neck Surg. 2010;136(9):866-871. doi:10.1001/archoto.2010.146
Images of the toys that have been recalled...