A personal golf launch monitor (or flight scope) is a great tool to have. It provides instant feedback on swing speed, carry distance, club distances etc. In addition, juniors love seeing the feedback and end up getting in more (and better) practice on the range! It can also be used to do your own ball fitting, compare different drivers, shafts etc.
We found the Voice Caddie SC 200 for $299, a great price for a good personal launch monitor.
A GPS watch that shows distances is a great option for juniors - especially younger ones that do not need a range finder or don't want the hassle of carrying one around. Our younger junior uses his Garmin all the time!
At only $119 the Garmin Approach S10 GPS Golf Watch is a great deal at Worldwide Golf Shops!