I personally don't see how Nintendo can be considered kiddy unless it is compared to other systems. But right off the bat not much about Nintendo is really all too kiddy. What makes it kiddy? The use of more vivid colors? The lack of blood/guns? The lack of AO games? Unless you live in a black and white world, just because Nintendo doesn't directly gear towards adults, it doesn't mean it is geared directly for kids. So yeah, Nintendo is "kiddy" compared to Sony and Microsoft, but when it stands alone, nothing about it is really too kiddy. The level of "kiddiness" is relative to other things. Anyway, that's my shpeel.
But it doesn't matter much to me anyway. Wii pwns in my opinion.