I would tend to agree with Sagenysd. I don't know how many kids I've seen in public with a GBA or a GBA SP. And yes, 90% of them seem to be playing Pokemon.

Now that's not to say GBA is strictly a kiddy system; I'm much older, and I am a huge fan of the Fire Emblem series, two of which have been released on the GBA in North America. Fire Emblem almost exclusively relies on strategy and planning ahead. There is a small amount of luck invovled, but it's certainly not something most younger children would enjoy.