I don't know a lot about it, but a couple of my daughter's 6 & 7 yr old friends and nephews are totally into it. Apparently there's so kind of figure inside of the magnetic balls. And when you "battle" you end up gaining new one, losing ones, trading etc. I imagine like marbles used to be a long, long time ago. My SIL is a teacher and is very particular about what games, etc. she'll let her sone play with, but she seems to have no issue w/ Bakugan, so I think it's o.k. You can also find some adtl info here:
http://en.wikipedia.org/wiki/Bakugan_(toys)#Game
I know my nephew ( he's 6 1/2) is really big into Pokemon too.
Btw- The Bakugan balls are pretty small, so you might want to be careful w/ your 5 month old.
sorry I can't be of greater assistance. GL!