I think the suggestion of a MPR is a great idea. The Micro Practice Rod is just a version of the original Wulff Fly-O
I could not afford the Fly-O. so I made my own version by using the same yarn. The yarn is known as "Gift Tying Yarn" and it used to be popular in the 1980's but and can still be purchased on-line with a Google search.
Pak it Products Gift Tie Yarn
The MPR uses Macrame Cord tied to Gift Tying Yarn. A 20 foot section of macrame cord alone can be used as the "fly line". Macrame cord is sold also as "craft cord". The most popular brand is Bonnie Craft Cord.
Or you can contact Echo
rods and buy the preassembled MPR line.
Instead of the MPR rod, you can use the top half of a fly rod or even the top half of a spinning rod as a substitute for a MRP. I used the top half of a spinning rod to practice indoor fly casting.
The MPR is a great way to teach children to cast.