Nit picking -

Teeter totters, a fixture of playgrounds up through the 1980s, seem to have disappeared in the 1990s in a flurry of excessive safety consciousness.

So, a few kids got fingers pinched (or broken) in the fulcrum. So a few kids might have gotten bumped hard by their brothers (or evil sisters). What's a little spinal compression?

Sources

Table 9: : Estimated Emergency Department-Treated Injuries Associated with Playground Equipment by Product Code, 2001-2008. 1243 (Seesaws or Teeter Totters) 41,094 2%