Steam engine derailing

[River]

I'am new to model railroading. Just bought a ho scale Echo Valley Express Steam engine set. I have a dog bone track set up. It is set on 2 inch pink foam. I bought extra 18 inch curves to complete the design. Running just the engine and tender it derails on the curves. The small wheels by the cattle guard does not make the turn. Any suggestions.

[Trainman203]

In the railroad world, the small wheels as a unit are called the pony truck or pilot truck.  The "cattle guard" is called  the pilot.

The pony truck be be screwed on too tight, unable to swivel side to side.  Something may be hindering the axle and wheels from turning.  The track sections may not be aligned well, giving the wheels a rough place to catch onto.

Check those points out and report back.