Kids' baseball gloves last as long as they need to: a few years. Because that's how long it will take for your kid to outgrow it. Investing megabucks into an heirloom-quality glove for an 8 year-old kid is insanity.
Now, maybe a baseball glove could be a treasured thing you hand down from kid to kid in the family or the neighborhood. But hand-me-down baseball gloves are a little nasty.
Your hand, which is invariably covered in lots of unsavory stuff (dirt, sweat, spit, sometimes sticky substances from the baseball bats) gets stuffed inside the glove for loooong periods of time, during which it sweats profusely. Being "gifted" with an "heirloom" baseball glove as a kid would have grossed me out. I would have enjoyed such a gift about as much as a hand-me-down jock strap.
I also hate to say this (because I like the idea of buying American) but unless you're playing a hell of a lot of baseball, $50-$100 gloves made in China also last a loooooooooooooooooooooong time if you oil them once a year or so. Unless you're playing baseball full-time, you do not need to spend hundreds of bucks to get something that will last you decades. Making a baseball glove is not rocket science. It's leather. Made into a glove.