Ukuleles seem to be the next big thing in our household.
First our eldest got one for her 15th birthday, then DD2 got one for Christmas. And when DS turned 9, he used his birthday money to buy himself the one below. He was the only one who would let me get a photograph of him.
Ukuleles are a nice little instrument for kids. They are light, cheap ( although don’t get the cheapest as they go out of tune as soon as you look at them) and easy to learn. They don’t sound too horrendous when being practiced but shaping the chords does make fingers hurt a little after a while, so it’s usually self-limiting. Don’t bother with books, just go onto YouTube where anyone wanting to learn will find all they need to know.