Hello,
How long has your tank been up and running? If it is still a fairly new tank I would avoid getting a snowflake eel for now. They can be very sensitive to water changes and if your tank is still cycling you might lose him to a spike. I have a 14" snowflake in my tank and he is one ODD critter. Even though they are fascinating creatures, let your son know that they are really seclusive and will hide most of the day unless hungry. I have noticed him going after some of the blue-legs before so I fed him more often and that seemed to keep him away from the crabs. If you are ready for a snowflake, make sure you test your water often to avoid any sudden changes that will effect him (I check mine every day....ammonia, nitrite, nitrate, sg, temp, pH)
How much live rock do you have? The more you have, the better chance he will thrive. If you are still setting the tank up and start adding live rock for a future snowflake, place it so there are ALOT of caverns and holes for him to roam around..that will increase his activity and allow you to see him more often.
Hope it helps ya