using easy books in the teaching of foreign languages to a 6 year old

My child is 6 since august this year. I finally decided to introduce books in his teaching foreign languages.
We kept the game of days / languages . MEaning - every day is almost another language.
Or in fact there are 2 days for French, 2 for English, one for Spanish and One for Russian.

This year, since I am mostly home, on leave, pregnant, I keep him some days at home. He omits the kindergarten but that is not so bad for him. He appreciates the time with mummy especially after so many years when mummy was working the whole day. And especially that soo there will be another child at home. And the my older son surely will be a little jelous.

Anyway, we keep on speaking a lot .. using techniques like -- ask for in the language to get it
see the dialogue
- Would u like a tangerine?  - I show the fruit to him
- Tak
- "Can I have a tangerine please"?  - i give the sentence to repeat , he is used to it, he knows already what to do , and repeat
then he gets the tangerine

and so for.. We also use the sentence... Polish please.. when I speak the foreign language and he doesnt get me inspite of trials... and gestures.. then when he says it -- I say in Polish what I said before in the foreign l.

But getting back to books

I do not push for it too much.. It is like one easy ex.. , one listening per lesson, mostly it is still the play time,
but he can write and read so the exercises are fun

I consider good books and I advise u :

for French
Alex and Zoe   

for English Bugs 1

for Spanish
Pandilla

for Russian 
Stupieni 1 

there are links when u go over the titles with ur mouse

all the best in ur teaching ! :)