Use them as car ramps. Let the kids experiment with which cars go further down the ramps at same level (big cars, little car, heavy/light).
Do cars go faster/further down a ramp that starts high or low?
Do the same with a variety of small balls.
Let them discover how other object go down the tube. Will wood blocks go down? Why not?
Use a bit of painters tape to help keep the ramps in place (tape to walls, table tops, chairs etc).