I can't wait to read LOTR to my (now four-year-old) son. Been looking forward to it since we started trying for a kid. Seriously, peak fatherhood moment. I'll savor it. That (and a few others are) on the embargo list: he's not allowed to see the film before we read the books. I wish I'd got Winnie the Pooh on there in time.
You're at a good time for The Hobbit. Strangely I find that Winnie the Pooh does not age well and is an awkward read.
The Wind in the Willows is good beginning around that age too.
I feel like winnie the pooh won't lose much from having seen the film version beforehand, but also the books had the kind of whimsical humour that I enjoyed a lot more in college than I did as a kid.