hello! i am diabetic and when my sugar is low, i stutter too. i actually go almost completely out of it depending how low i am. i get really confused and disoriented. about the testing, depending on what meter you have, you can test other parts of the body. i know some meters let you use your forearm or toes. just check out different meters and talk with his doctors about the different options he has.
I know that there are some meters that use tinier drops of blood than others, and also that people can use sites other than fingertips with some meters (usually the ones that don't require a large blood drop). I have read, however, that sites other than fingertips can be less accurate. As to how different the glucose reading would be, it probably depends on the meter and perhaps on the size of blood drop. Fingertips are used most often because the blood vessels are near the surface and you don't get as much other body fluid mixed in with the blood drop (although I have also read that if you have to squeeze very hard, you may end up with other fluids mixed with the blood and may have a less accurate reading than if the blood drop pops up easily). Maybe that information will at least help you make an educated decision. You may want to do some research on meters that require tiny drops of blood, and maybe also on the accuracy of testing using other sites.
As for long-term brain development, I do know that doctors tend to keep blood sugar levels in small children slightly higher than in older children because the brain IS developing and low glucose levels have been shown in tests to cause some memory loss in adults, and therefore may be dangerous to little ones. The stuttering when low or high is because during those times his brain is starved for its primary fuel, which is glucose. When low, his brain doesn't have glucose to fuel it because he has too much insulin at work, and when high, his brain is still being starved from its required glucose because the body can't use the glucose that is in his bloodstream due to inadequate insulin. Both can cause the brain to temporarily not be able to work properly, and so confusion, speech problems, etc. can temporarily be evident when his sugars are 'off'. It sounds like you are watching it carefully, and as long as you are doing those frequent tests and are adjusting his levels throughout the day, he should be fine. I grew up as a type 1 and managed to be a valedictorian in spite of lows and highs in childhood... your good parenting will help protect his brain as it develops. I do wish him the best and encourage you to keep up the good work. It will get easier as he grows older.