[ars]

Too late - they already did it. Unless you are implying you hover over them no matter where they go.

Most parents will sit on the side and watch their kids. They can remove the tire material from their mouths, but they can't stop it from entering in the first place.

[WendyTheWillow]

Most parents don't take their children to playgrounds where the likelihood of putting toxic materials into their mouths is high.

Also, having watched many a young child, this isn't normal behavior for children you leave alone to play on playgrounds, precisely for this reason.