Hey,
Welcome to PBF! Anyway, to you question. Since they're young, and you're not sure if they'll like the sport yet, there are two basic options to look into.
A) A spyder package (includes everything a beginner needs) or a spyder clone package. The difference between the two is nothing really, same basic design, just different names. (please note some people actually believe that not to be true, so be careful for the posers, lol)
B) A tippmann power pack. This includes the same equipment as a spyder package.
There has been, and always will be a fight between which is better. Personally, Tippmann's are the best starter markers out there. They take one heck of a beating, and they can go without being cleaned longer then most beginner markers out there. Very upgradable, and very affordable.
Spyder package on the other hand is great for older people that want to learn all the little parts of the marker, and they like to tinker. They're also great starter markers, but they can be slightly problematic since the parts typically used in them are cheap and tend to break. Upgrade parts aren't that much money though, so it's really easy to make a kick ars one.
Maybe since they're both starting out, you can get one of each, and let them decide who likes what more. For further information on upgrades on any type of equipment, check out the respective sub-forums on here for a better idea. Remeber to read before you post, as to not repost something that has been answered a billions times. Tends to make us happier when ya do that.
Good luck man, anything you need let us know.
- Brian