You know, one other way to prepare your 5-year-old for learning English is to get a couple of DVDs with English soundtracks (you may already have some on hand). Cartoons or favorite Disney stories (at 5, your child may be a little old for Teletubbies, but that's a "universal" show that works well) - and just start playing the English soundtrack.

Children pick up languages faster than you realize. If there are songs on the films, so much the better. I know a Spaniard who learned English by listening to American rock 'n' roll songs when he was a kid.
Cheers,
Bev