Howdy Adam.
You have been given some great info here.
Now if you think for just a min. What does a 10 year old boy like? Questions man questions. ????
What are the fish eating? Why to you use flies? What color is the water to the fish? Does the sky still look blue to them? Will worms work better? What do we have to eat? Can I eat raw fish? Can fish breath out of the water? Will a blue fly work better that a red fly?
Of course you can not know everything.
You might try this. Get a sample net to find out just what is in the water. NO net, a hanger and a pair of panty hose. White is best. Hold the net down stream and shake a rock or two. On a pond drag it over a weed bed. Now if you can get him there the day before the trip or you can go early and sample the aquadic life bottle and use it to show what the nymphs look like. It will connect the fly to the food that fish have to eat.
Take time to let him skip a rock. Get his feet wet, Be a Boy in your mind but remember to keep it safe. Please. keep it very safe.
Have fun learing all over again. It is Great.
ol Al

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Ol' Flysoup
Flycasting is as easy as flysoup