Yes, if it gives the child pleasure and helps the child connect with the world in a meaningful way, then the "obsession" looks healthy and useful to the child to me.
We all view the world through lenses that make sense to us. If your child's lens is math or cars or dinosaurs...so what? What does it hurt?
DS7 has been serially obsessed with letters, colors, building equipment, cars, race cars, and now Transformers. (I may have missed a couple, too!) Every one of those had its trying moments for me, but they were never bad for him. He learned from them and loved them, just as fitzi is describing. They were a springboard to making sense of the world. In my mind, that's a positive thing.
It also looks to me a lot like the sort of specialization that we adults do. I took math, but I don't love it. I LOVE literature, so that's what I'm doing for a living. It's my passion. In adulthood, we think of having a passion for what we do as a good thing, not a bad thing. So provided these kids don't dig in their heels and refuse to do *any* math (or whatever that's not their passion)--and most don't!--why penalize them for finding out about healthy, intellectual passions early?
I think of this sense of focus as being part of my son's makeup, like his introversion and his eye color. It's easier to accept it and even embrace it so we can use it for his growth and development than it would ever be to try to change it.
Stepping off my soapbox now...
