i think a cheapish keyboard would be good but i'd expect them to lose interest quickly unless they have a program to follow
but it's good to plant the seed and hope they come back to it later if that happens
i wouldn't spend a lot of money just yet maybe?
learning an instrument can take a lot of dedication and young minds easily wander
i tried to learn guitar when i was about 16, bought the whole setup and it lasted about a month before i gave up
just didn't have the patience , was expecting to be Van Halen in no time
i came back to it about 8 years later and dedicated myself and finally got somewhere. so glad i did
also reminds me of buying my niece a half decent acoustic guitar when she was quite young, maybe 15. it was a proper one for smaller hands and all
it got a few uses then gathered dust. every time i called round it had another bash or something dinged until finally it got busted open beyond repair.
it broke my heart watching that thing die