Boy#1 to the Knitting Darkside!
Your best approach with Boy#1 is small achievable goals, cast on about 5 stitches in DK and let him knit until he gets bored. He will either have a teddy scarf or the first of many squares that can be joined to make little juggling cubes. Frustration and randomly gained/lost stitches are a common starter error (especially when they are under 3 foot tall) a good cure is to help him to change colours every 2-4 rows. This means he can focus on his next colour choice and he can see tangiable progress. It also makes your job easier as you can give him positive, targetted feedback (wow your green stripe is much better than the yellow!) rather than feel like he is spending more time asking you about it than actually knitting.
Let me know how he gets on