I'm a generalist. Professionally. Personally, I'm a bit of a specialist, but - hrmhm - that's just between us. No, I'm a generalist librarian - a librarian who serves both adult and juvenile customers. Most public library systems don't expect their professional staff to be proficient with teens, children, adults, and seniors, but the one I work for... does.
As you might imagine, librarians in other systems sometimes scoff at this arrangement. School librarians in particular are kind of amusingly horrified.
Generalists are expected to maintain at least a glancing knowledge of the adult best-seller list and genre fiction (I can name 3 Amish romance authors off the top of my head - we all can!) and stay abreast of trends in juvenile and young adult literature. It's admittedly kind of a lot. You read a lot of e-newsletters.
But the up side is that when I read an adult novel, I notice when that book includes teen or kid characters who are going through teen or kid things, and I file it in my head as possibly good for underage readers. Books like this are called Adult Books for Teens, and there's a whole blog over on SLJ devoted to them. There's also an award, the Alex Award. In an interesting boomerang effect, if you are an adult who likes books that are both well-written and fast-paced, you might mine these lists for suggested reading. I do.
By the same token, when I read children's literature, which I mostly do, sometimes I notice when the characters, the setting, or the obstacles they confront would resonate with the adult readers I serve. There's no blog for Children's Books Recommended for Adult Readers, but maybe there should be.