...one thing I forgot,

The age is crucial. Here in the US, and I think this is universal, 8 years old is a very important benchmark. There is something about the brain development at this age, concrete/abstract, that makes it much easier to read notation after this age. I found that you can teach an 8 year old in one year what it takes two years to teach a 6 year old.

When teaching younger ones, the approach should be much more imitative and not require reading. That's why the Suzuki method is so successful. You might even check out Suzuki for piano, but remember, parental involvement is crucial for its success.