Let me start by saying that I'm finding this thread thought-provoking and possibly even useful, and am arguing as a way to clarify my own thinking. I hope everyone reading is doing so in the same spirit; I certainly don't mean to offend.
Oh, I meant "finished with HP," not "outgrown HP." Also, I have actually read these books, so it wouldn't be like I would be asked for more details and have to reveal that I didn't know what I was talking about. But I didn't say that because in most cases I might not have read the book. FTR, though, my mom is a children's librarian and my friends generally know I'm a kids' book nerd, so there is that.
(Yes, I assumed that was what you meant actually.) You're probably fairly safe, then, but the suggestions might not work so well for someone else :-) (In actual fact, I too have read these books, but I could have picked something I only knew about from DS.)
But yikes, you would recoil? It seems really arrogant to you? Huh. I wouldn't find "x series is good for kids who have finished that one" to be arrogant in the least.
Yes, I'm afraid I really would. To me it's like any other case where someone who, as far as I know, has experience only of her own children makes blanket statements about children in general. Try "Children need regular bedtimes", "Boys so love running around", "Children who like potatoes like carrots, too". (I mean, I might not notice - most people, me included, slip into talking in generalisations sometimes, there's one ;-) - and if I did notice I might think you were daft rather than arrogant, but I don't find it advisable to generalise like that.
Suppose, for the same of argument, that you're recommending a book about which the only thing you know is that your own child loved it shortly after the HP phase. Now imagine how the conversation might go on in each case:
Version 1:
Her: blah blah Harry Potter blah blah
You: My son loved [book] just after his HP phase.
Now, as far as I can see, the only possible difficult continuation is:
Her: Ah, that's interesting. How old is he?
at which point you're in a slightly tight spot, but at least you've been open. I'd probably go for:
You: He's a bit younger than yours, but it sounds as though they have similar tastes. [And change subject ;-) ]
Version 2:
Her: blah blah Harry Potter blah blah
You: [Book] is good for children who've finished HP.
Her: Ah, that's interesting. Why do you say that?
You: Well, my son loved it, anyway. [Nothing else you can say, by hypothesis]
Now don't you feel a bit of a prat, having been pushed into revealing that your general statement was based on one kid? And you're still open to "How old is he?" at this point, so it's not as though you've gained anything...
Version 3:
Her: blah blah Harry Potter blah blah
You: I've heard that [book] is good for reading after HP.
Her: Ah, that's interesting. Who did you hear that from?
You: Err, my son. [Nothing else you can say, by hypothesis]
And again, you feel like a prat, and you're still open to "and how old is he?".
All in all, looks to me like "O what a tangled web we weave, when first we practise to deceive".
The only nonarrogant way is to talk about your kid reading it??
I don't say that's the only nonarrogant way, but TBH I find the idea that one should be scrabbling around for a way to conceal the obvious underlying fact, that one's own child enjoyed the books, sad and faintly ridiculous. The concealment "smells of the lamp" to me, since it's so much more natural to say staightforwardly that your kid read it, if that's the case, and when you tie yourself in knots to conceal some piece of information, IME all too often it comes out anyway and the result is worse than if you'd been straightforward in the first place. It may well be partly just that I'm not good at doing the concealment, I admit!
