Hi there,
I know nothing about the business side of it, but I know what I'd like in an ideal bookshop:
Marked display copies for all age groups in a corner, so I don't have to worry constantly about the children ruining brandnew books.
Knowledgable staff who can advise me if I want advice, but who let me browse the shelves if I prefer that. I used to go to a bookshop where I felt the staff were approaching me the second I entered the shop in a way that I found really intimidating, and they somehow made me feel that they didn't like me having a look around on my own. I avoided that shop after a while...
At another very good bookshop on the other hand, staff advised me in a very polite and unobtrusive way when I asked for a fairy tales book. They had various ones in stock and pointed out the differences and then left me in piece and quiet to have a good look at all of them and choose one, and despite the fact I bought one of the books there and then, I felt under no pressure to do so, and this is what I like about a shop, and then I'm likely to return.
Don't just have the obvious titles displayed which I think most people would be more likely to buy in chain store as a buy one get one free. Have unusual books but not only in an expensive hardcover copy.
Have quite a selection of books. I end up leaving one very small local bookshop empty handed no matter how much I want to support them as there is so little to choose from and the shelves look so bare that I don't get inspired at all. I know they can order anything within one or two days, but what if I don't even know what to order in the first place?
Have no videos and DVDs, or, if you must have them, at least well hidden from the children. Otherwise all they want to buy is... videos and DVDs, and it's far more difficult to steer them towards the books.
Having said that, do have story tapes/CDs and audio books, and maybe a place where the children can listen to some of them with headphones. I visited a bookshop in Germany that had these facilities, very easy to operate by the children (literally put on the headphones and the story would start, and the cover was displayed, and the seats child height). I have to admit though, this was quite the opposite of the small independent bookshop, so I suspect it's something only larger (chain stores) can realistically have?
Also, hopefully enough room to at least get through with a buggy and/or a space where to leave it without it constantly being in the way of other customers.
As an extra, I also always appreciate unusual but not overly expensive greetings cards and giftwrap, and maybe bookmarks, obviously in this case designed for children, as I often buy books as birthday presents and it's nice to get everything in one place.
Maybe also a noticeboard (for private buy & sell, or advertising local children's events or news etc.) for customers or organisers of local groups (such as toddler music classes etc.)? You could charge a small fee and make it clear how it works so that people actually dare to put something up. I find nice noticeboards are very rare and I'm sure it would personalise the shop more (opposed to the rather anonymous chains) and would generate more customers who maybe want to check out the noticeboard and end up buying a book...
If possible, have something comfy but cleanable to cuddle for the children. As some large teddy bears can get very dirty after a while I'd look out for something either washable or not too expensive and replaceable.
Some seating but not just for the children, but also for the adults (which can easily be forgotten).
Something obvious but don't have stairs. I remember a chain store moving up their childrens section to the first floor, and initially having no customer lift (eventually they did have a lift).
If the shop is in the London area or another area where other languages than English are spoken as well (?) have some books in other languages, too.
Hope you can fulfil your dream!