Hole Punch or Something to Make a Hole in the Cardboard Tube
Hot Glue Gun
Paint your cardboard tubes various bright colors. Cut C-shapes out of one of the tubes to create both the top of the engine and caboose. Paint those accordingly. Also cut a C-shape out of the skinny cardboard tube and paint it the same color as the engine. The C-Shape tubes will arch nicely around the toilet paper roll.
Once dry, hot glue the tops of the engine and caboose in place. Also, hot glue four plastic lids on each cardboard tube as the wheels of your train.
Punch small holes into the four “corners” of each tube. These are your attachment points for the yarn. Cut the yarn to length.
Weave the thread through one tube and another tube to attach two tubes together. Tie a knot. Continue the process until all of the cars of the train are connected.