I know LOTS about paintball
I have several questions.
First, what is the age of your kid? Second, how much of a budget do you have to spend?
Those are the two most important questions to ask. The first is because younger kids will be harder on their guns and less likely to maintain them properly. As such, I highly recommend sticking with rentals for awhile.
If the kid is old enough that you as a father trust to respect his marker and take care of it properly, then the second question is far more paramount. If the kid is still fairly young, but you REALLY want him having his own gear, then getting a tank of a marker and a cheap one is going to my highest recommendation.
With paintball, if looking for all new equipment, one can buy everything needed for under $300 pretty easy. From there, the sky is the limit when it comes to paintball gear.
For the low end with a "tank" of a gun, get a tippman 98. They are cheap, practically indestructible, and require very little maintenance. A tippman 98 with a gravity fed hopper, cheap max, and small CO2 tank will not cost all that much. Many sites provide a starter package with everything you need with this gun for $150 roughly.
http://www.tippmannpros.com/p-250-tippmann-98-custom-ps-ultra-paintball-marker-mega-gun-set.aspx
This setup will work as a good starter setup and teach your kid a bit more about respecting their equipment, let them learn maintenance, and still have fun.
I will say that the tippmans are NOT performance markers. Your kid will not be the envy of all the other kids out on the field with that setup.
If your kid is a bit older, willing to keep good care of his equipment, AND you got a decent budget to spend then you might want to consider some other options.
Personally, you'll see people recommend those cheap Spyders and Kingman markers. I say don't bother. Those markers are typically a nightmare. They have shooting problems quite often, lots of maintenance is required to keep them going, and really don't perform all that well for the money. They also typically have their own proprietary parts that prevent any sort of after market upgrades or replacements when things break.
Now, if you are deciding to go with something beyond a tippmann for a purchase, the next question to answer is what TYPE of gun design would you be more interested in. There are two major types of gun designs. Poppit style valve guns and Spool style valve guns. Each has different charastics and pros/cons. Let me explain the differences.
Poppit = slightly older technology, but more mature. Poppit guns typically require less maintenance, need replacement parts (o-rings for example) less often, are more air efficient (requires less air used per shot to shoot a ball out of the gun at a specified velocity), and are typically cheaper.
As for cons they are louder guns. They usually have a bit of kick/recoil associated with them (nothing that will make the gun jump out of your hand but enough to be felt when compared with spool guns). A chopped ball while playing may prevent the gun from firing again until the broken ball is cleaned out first. Can be heavier in weight especially the older stacked tube designs versus the newer inline poppit designs (which are lighter but usually much pricier).
Spool = newer technology guns that are smoother, less recoil, and quieter guns. They are less air efficient because they use more air to shoot with in addition to a bolt that smacks the paintball inside the breach of the gun. Because they use more air, a broken ball that may occur while playing can be forced out completely with the next shot much easier than a poppit gun. So no stopping while playing to clean out the barrel if a ball breaks usually with a spool gun.
They are less air efficient, although the really high end versions of these spool guns are pretty darn efficient when compared to poppits if only barely less efficient. Those high end ones you pay for. Spool guns typically have an oring or two that are major workhorse parts that break down far faster than any oring used on a poppit gun.
So knowing the difference in types of guns I'll recommend guns from each type from here on out based on price range. For a starter marker that is decent I suggest one of the following.
Azodin Blitz at $169
This is a great entry level poppit bolt style gun. It's a bit loud but reliable and sturdy. Maintenance is easy as well. It comes with many features found on pricier guns and comes in a variety of colors to choose from.
GoG eXTCy at $250
This is about your best entry level spool valve gun right now. There are a couple cheaper spool valves, notably the GoG eNMy/eNVy, but they lack a few key features such as "eyes" that are little lasers in the breach of the gun that sees if a ball is seated correctly before allowing the gun to fire. That one little item makes a vast difference in your gun. It prevents ball breaks by quite a bit. The only bad bit is That the gun is not made from 100% milled aluminum, but instead from composite materials. This means the gun is light, but not usually as sturdy.
For the next step up in performance you have the following I recommend.
Dangerous Power G5 at $329 or
Planet Eclipse Etha at $349
Both of these are great poppit style guns. Both are built very well and a come with a ton of features for good competitive play in paintball. You can't go wrong with either choice.
Up until recently, the next Spool valve gun up from the eXTCy was the Proto reflex rail at $500, but a recent released gun has changed the all that.
Valken Proton at $325
This is a spool valve gun with all the features and quality of any of the higher end spool valve guns. It has no macro line, high efficiency, accurate, completely milled from aluminum, sturdy, easy maintenance, light weight, and smooth shooting. The downsides are that it doesn't look like much, only two color variants right now, louder than higher end spool valve markers, and reliability is an unknown factor since they were recently released. Beyond that, these are fantastic spool valve markers that compare favorably with anything else out there. This gun won't turn any heads in the looks category, but it will perform with the best.
If you REALLY want to spend more money, there are a TON of paintball guns from various companies trying to get your dollars. Anything past more expensive than the $300 guns I listed don't really add much more performance for the money. You are mostly paying for the bling/wow factor of those guns.
One thing to keep in mind though, is that when you buy any of these markers I've recommended past the tippmann, you will ALSO have to factor in costs for a few other essential gear items. These include a tank, hopper, and mask. You can not play without a gun, tank, hopper, mask, and of course paintballs. Beyond that there is plenty of other gear you may find nice to have, but aren't required such as specialized jersey's, knee pads, and other items such as that.
When it comes to tanks, the price is pretty consistant. Tanks come in two major varieties. CO2 and HPA. Tippman's use CO2 and everything else you pretty much want to stick with HPA. After that, it's all about determining the capacity you want in the tank. The standard competitive tank is a 68i/4500psi and that runs around $150 pretty much new. A slightly cheaper approach is to use a lower psi tank at 3000 psi, and smaller volume at 48i. Those run about $50. Just be aware that most good guns will go through a 48i/3000psi tank in a few minutes of continuous firing.
Masks can range in price dramatically. Cheap masks will run about $20 and the good ones up to $150+. Higher priced masks are typically more comfortable, provide various lens inserts that allow you to change your lens based on the weather for better vision regardless of the environment, lighter, and are made with softer materials to allow balls to bounce off easier instead of breaking every time on impact with the mask. Really I recommend going into a local paintball shop and trying on various masks with your kid to see what they like best and what you are willing to pay for in terms of features of the masks.
Hoppers also come in wise price range. Prices go from $3 for a gravity fed hopper I will say you MUST buy as a backup always, up to $250 for some of the high end force fed hoppers. Cheap force fed hoppers will run you about $40 from sport stores. They don't feed all that much faster than gravity based one, usually go through batteries quickly, break paint more often, jam up more often, and usually don't load all that fast. Better hoppers are a must for competitive play.
The basic competitive hopper is going to be either the
Empire Halo at $85 or the
Pinokio PL230/400 at $90
Either of those hoppers will do just fine with any gun.
I hope that helps make your paintball playing decisions easier. If you have any more questions feel free to ask.