Another alternative for getting kids interested in fly fishing is a cheap Tenkara rod with floating line. I picked up a couple of these 8 ft rods for $11 each on Amazon:
https://www.amazon.ca/gp/product/B00...?ie=UTF8&psc=1
I added about 8 ft of floating line from the back of an old damaged Weight Forward line and taped a couple of bent paper clips to the rod to hold the line and leader. I had my neighbour's 2 grandkids - ages 6 & 7 - roll casting the 8 ft line with a 4 foot leader in 10 minutes. Once they become a bit more proficient, their father can put on a bit longer floating line. The Tenkara rod takes the reel and line management out of the equation for beginners.
Surprisingly, the rod cast decently and I set one up for myself to fool around with on smaller streams. For the price, I figure I'll get my money's worth if they last the season!
I had also given those kids a bubble float and some dry flies to use with their spinning rods last year. They both caught trout using the float and so were interested to try the Tenkara rod this year.
Ken