You'll want to move him/her to a bigger tank as he/she grows out of it. They typically get to be 8-10" long. I own a female myself, abd have her in a 20long, that's enough for one gecko. These geckos can live around 20 years so be prepared to take care of it well. Some good info can be found at
The Leopard Geckos Site
Also do a search on leopard gecko care, do as much reading as you can.
And getting a book or two on these geckos is also a good idea.
Avoid hot/heat-rocks, they will burn your geck badly as they can reach 105 degrees F. Leos should do well with a heat source that's in the range of 85-95 degrees F.
Decent heat sources are the red incandescent spotlights and regular incandescent bulbs around 40-50watts. Regular incandescent bulbs can stay on in daylight hours, then the red spotlight can be switched on for night.
Floodlight fixtures can be used for these bulbs, and you can get some cheaply at any home improvement store. That's what I did, because as you'll soon discover, petstores offer equipment at rip-off price ranges.
Please also get a full spectrum daylight florescent tube for the daylight hours, I suggest this out of experience. Because I had often read that leos did not need this light because they are nocturnal. Well, I went about 6 months without it and her health deterioratted, she lost weight, her eye began to swell for unknown reasons, and her coloring was dulled. After I took her to a vet and put the light back on as she suggested to me, within a few weeks she had gained weight back, her color began improving, and her eyes are starting to get better. I'm currently still treating her for the swollen eye membranes, but as my vet said to me, "Reptiles take a long time to show sickness, and take a long time to heal." So please avoid the mistake I made.
One note on substrate, use newspaper. It is the most steril material there is to use as substrate and easier to clean than sand or wood/bark chips. With sand, dust will accumilate, you will never entirely remove waste material, and it is not as digestible as marketed. Dust can cause respiratory & eye problems, and internal blockages. Same goes for bark/wood chips. BTW cedar is toxic to reptiles. Newspaper may not give a very appealing look, but you will save yourself grief and money by doing so.
Rocks and hiding places made special for reptiles and small animals are all good additions to the gecko's home. Even though you may not see it often, they feel secure if they have somewhere to duck under and sleep the day away. Goo luck with your new pal. And make sure to have your son be very careful handling it!~Angela