As I've mentioned before, I do the collection development for the children's room chapter book series. I've got the computer doing a computation on just how many books that is at the moment (minus the hundred or so on order and about to be ordered for July).
3506 Regular Collection
436 New Arrivals/On Order
1359 Paperback books (we're slowly moving those over so they'll be just in the regular collection but with that many, it'll take ten years or so)
Total: 5301 (minus a few that have probably gone missing)
A large number of those are books in series--ranging from Lloyd Alexander's Prydain Chronicles to Animorphs to Tiara Club to Harry Potter. There's a wide variety of topics, time periods, age levels, book thickness. Kids love series. (So do adults, for that matter, or some of the more popular mystery and romance novelists would never have made it very far.)
With the care and feeding of the collection comes the making suggestions responsibilities* and that means I take home piles of books. The houseguests who've visted can attest that the "library basket" in my kitchen is overflowing--all the time. I rarely get to read anything more than a picture book at work and I feel severely guilty when I actually stop and go through some of my chapter books more than a brief skim. But how to know what to suggest?
I read the first books in series. I've found that it's usually enough to give me a sense of the series, to know what a child is referring to when they coming looking for the "owl" books or the "pet fairy"; I have a sense of storyline, characters, grade level, can discuss with involved parents whether it would be a good fit for their child, etc.
This baffles some patrons, who are hurt and offended that I'm not reading every single book in the series they most adore. "If you'd only read the second/fourth/fifteenth book" some have pleaded. I'm apparently committing some crime by only deigning to read the first one or three books. Sometimes I'm gentle but often (especially with adults) I'm blatantly honest--I don't have that much time in my life. I have piles of books at home waiting to be read, a few of which are even "adult" books rather than written for those sixth grade and under. On a good day I can squeeze in a couple of hours of reading, but good days are coming few and far between right now.
It's part of the job and I enjoy getting to see what new children's literature is out there. I consider it a testament to really good authors when I say yes, I've read the whole series (and wasn't 8 when I did so). I've praised Flanagan's Ranger's Apprentice and Springer's Enola Holmes series before and I'm caught up fully with Enola, though Book 5 of the Ranger's Apprentice on CD is waiting at home for me. I also just sat down and charged through all the new books in the American Girls series, but that was an hour and change of reading...
Such it is and with literally hundreds of new books coming in each year--I unfortunately can't read them all. When I can pass on a series, it lets me get to those rare gems that aren't a series. And really, life is too short to keep reading books I'm not fully invested in.
*in library speak we call that "reader's advisory"