Many of us have been introduced to action figures from an early age. At first maybe we just got to play with our friends toys but eventually a moment came where we liked a character enough that we bugged our parents for it. The interesting fact I have noticed these days is that much of what is created for television is based around numerous characters which are then meant to be collected by the kids. It is marketing from day one and thus some of the story lines completely do not make sense.
Around when American comic book heroes were really strong on the airwaves came Dragon Ball Z. It quickly gained a loyal following as it was different and also had story line that did not end at each episode. It was a very long, well thought out concept and kept many glued to it for years. One of my buddies from graduate school would actually run home to watch the new episode and it always made me laugh. In Japan this anime has been around for much longer and it was already extremely popular there especially among the Anime geeks. Many figures and other products have been created around the brand and sold quite well. Many of the older Dragon Ball Z Action Figures as well as Godzilla Action Figures sell for very high prices these days.
The one thing that I would be careful of is buying the Chinese copies which are sold as originals. It is a complete waste of money as they are not worth anything but can go for high prices online. This has always been a problem in the collectibles industry but now it is very predominant when it comes to action figures.
The research that you do now will save you a lot in the long run.
Your kids will probably want their own copies so be ready to buy a second one. I have done this for years with comic books as one of them is for the collection and the other to read. It might get hard if you are looking at an item worth a few thousand but that might be a time where you just buy it and put it away.
If you are able to, try and find other collectors in your area. Others with the same interest can possibly give you some great advice or even facilitate beneficial exchanges. I have been extremely lucky as I have got real great deals on my dragon ball z action figures before they became in demand. Some of the items I bought in multiples and now have three or four of each in my collection. Hopefully this will pay off even bigger in the long run and has paid for quite a few vacations already. It is definitely a great idea to buy some of these action figures and enjoy them even if they do not make you rich.