Over the years it has been amazing to see young pupils start guitar lessons. When I started teaching guitar full time 23 years ago the average age of a young person starting out on guitar was probably around 11 years of age and we never had any 5-year-old pupils.
Now the average age of a guitar pupil is down to 9 years of age and we have 5-year-olds starting guitar all the time. With the 5-year-olds that start guitar lessons, the learning process is very slow and the lessons need to be more about fun ie. a few minutes playing the guitar and then some silly dancing while I play and sing. Over time the silly dancing becomes less and less as their concentration improves. After one year they might only play 3 easy chords but that's ok. They may hardly ever practice either but as long as they enjoy their lessons and their guitar teacher it's worth pursuing. By the time they at 10 years old, they could be playing and singing in front of an audience and I've seen this many times with pupils that I have taught guitar at a young age.
My advice would be to start with ukulele until the age of 8 or 9 but that's another story for another day.
I hope you found this piece informative and interesting.
Small guitar information.