I really liked MK_Design's Gravitrax Roller Coaster piece, but I was afraid that in the hands of a child it would snap too easily, since a good portion of the ramp is suspended above the tile without much support.

I added some vertical ‘pillars’ to the design that will toughen it up a bit.

Note that these pillars don't replace the supports used when printing the model - it's more of a strength increase.

Use tree supports from the build plate and they'll come away easily and pretty cleanly.