So how do you try for Eton then?

[Newyearchanger]

I read that you can try common entrance at 13, but I also saw comments about putting a child's name down.... What does that mean?

How to prepare for logic test for these schools ? Any book(s), online material ?

For the Eton pretest, you basically don't. It's a unique test and there is nothing targeted to prepare for it.

To practice verbal and non-verbal reasoning generally, try the books published by Bond.