There are some frum veterinarians (do a bit of Googling and you’ll see.) I don’t know how they can do it. But I’ve heard some poskim allow spaying and neutering nowadays.
Anyway, I think WinniethePoo is right, that it’s not really a problem in practice; by the time they’re old enough to seriously think about careers they will no what’s not appropriate. There are few non-frum careers anyway that a small kid would know about.