The problem with the "Nintendo will get the kids market" is often times they don't when it actually comes to consoles.
Young boys are more fickle than even teenagers and adults when it comes to home consoles. By the time they get to 10-12 years old, they start wanting to play games that older kids are playing and go out of their way to not play "kiddie" looking games in some cases.
The other problem is if you have an 8 year old in the household, but they have an older 13 year old sibling ... you're going to end up buying the Sony/MS console more likely than the Nintendo one because the 13 year old will raise a bigger stink about which console they want (the "cool" one) whereas young kids aren't as picky about specific game consoles per se.
They're fascinated by video games in general and as long you grab them a LEGO game or some other kids brand software they recoginize they're ok with that. So as a parent you end up getting the Playstation or XBox instead of the Nintendo because it will save you the headache of having an upset 13 year old. The 8 year old is happy either way.
I remember thinking during the GCN/PS2 era that Nintendo should clean up with the kids market. After all, the GameCube had a cute colorful design and had a lot of family friendly titles like Mario Sunshine and Animal Crossing, but it absolutely got destroyed even for the kids market by the PS2.
The Wii's explosive initial success IMO came largely off the backs of ADULTS, not kids. It was the hip/trendy thing to have at house parties for a few years for sure.
