Teaching very (very) young kids

Good evening from Japan,

I usually teach Business English/ESP and have absolutely no experience teaching kids.

A Japanese friend of mines have 3 kids (18 months, 3yo, 5yo) and wants me to teach them some English.

I'll probaby use OUP's First Friends or Tiny Talk with the older kids. But the 18 months toddler... frankly, I have no clue.

Any suggestion(s)? Any textbook/activity book you recommend?
First Friends or Tiny Talk are both made for kids ages 3-6. I really don't know what to do with the little one.

Thanks,
Larry

There are some sites for young learners here, including very young learners, that might help:
Young Learners - ESL Web Directory - UsingEnglish.com

I would not try to teach a child of 18 months, I would play with the child, speaking English to it as naturally as I would to an English child of that age, sing nursery rhymes, and, with picture books, tell simple stories. I would, for 5-10 minutes watch episodes of children's programmes on YouTube with the child.

That's what I would do if I were asked to 'teach' a young child. It is what I have done with my honorary Czech grandson from the time he was born. I did not pressure him to speak English, but encouraged him to do so when he seemed to be interested. Now, at three and a half, I am putting a little pressure on - he knows that if he wants some šunkou a sýrem, for example, he won't get any unless he asks for ham and cheese.

He understood English almost as soon as he understood Czech, but did not really start to speak any until a couple of months ago. Now he is beginning to speak it more and more - not because he is learning a foreign language, but because he wants to communicate with me.

Yes, just play with them, keep them happy, use English, show them objects and say their names, praise them in English, and ensure they have fun. I'd attempt no academic programme.

I used to like SuperSimpleSongs
They had some stuff to do with very young learners