soprano ukulele. They're not too expensive but a lot of people like the sound, even compared with more expensive models. It's a really fun instrument and my kids like to play it too. It seems like it shows up in a lot of lists as a great beginner ukulele. There are some chords that are a little difficult for me to fit my fingers into the frets though. For a 12-year-old that's probably not an issue.
My next Ukulele was a concert size that's a little bigger, so my fingers fit a little better. It's a Kala brand. I swapped out the high G string for a low G to play some of the songs I wanted to (like the famous "Somewhere Over the Rainbow" by Israel Kamakawiwoʻole -
https://www.youtube.com/watch?v=w_DKWlrA24k), so it's got a nice, rich sound to it now.