I'd get a quality revolver...so you could shoot 22 short, 22 LR or 22 shotshells. (Or 22L if you happen to see them).
A Ruger Single Ten; S&W 34, 617, or 63 are what we use for young/inexperienced people to shoot.
But, when my kids grew up and moved out....they picked the MKII's out of the safe for their adult .22's.
At the end of the day, I think it is more the time they spend with you learning than the platform you pick out.
YMMV
