Those are plastic SPARKLITES.

By sparks we mean each turn of the wheel producing a light show.

Properly speaking, the flints are the small rods being sparked by the wheels.

Yes, a poorly made wheel can decompose. Even SPARKLITE suffered from a small batch of defective units they made good on.

My brass sparklites are Vietnam era, and have held up better than my other stuff from that period.

Keep them clean and dry and they should last a long,long time.