гойдалка; дошка через колоду

seesaw(noun)

a long flat piece of wood, metal etc, balanced on a central support so that one end of it goes up as the other goes down

The boy fell off the seesaw in the park.

гойдатися на дошці

seesaw(verb)

to move up and down like a seesaw

The boat seesawed on the crest of the wave.