Teaching a 6 years old
Most of my students are adults, I have taught children with a curriculum so I would like to get more advise about teaching a 6 years old and maybe if you know books or websites with good materials.
From my experience, children learn fast but need constant reinforcement to prevent them from becoming inhibited. Immerse your child every day if you can. If your six year old is in an English environment, for example, refuse to speak English during "class time" and be consistent. It takes a lot of persistence to keep moving things into the new language, but eventually it pays off. You didn't say if you are fluent in the target language for your child.