First of all, I'm really glad we have a diligent teacher like you.
I'd like to thank you, as a Japanese citizen, for your sincerity.
Please allow me to introduce myself.
I'm an English teacher at a 'cramming school' called 'juku,' and I've been teaching students (mainly) aged 7 to 16. And...I know how hard it is to teach English to little kids, especially when they are beginners.
It's virtually impossible to expect them(your little kids) to produce grammatical English sentences as they've never learned English grammar, and it would be extremely hard(almost impossible) for you to teach them English grammar as they hardly understand your words. They are not learning English in the natural environment (where it is spoken/used in everyday lives).
So...all you can do right now is...
1. playing games
2. repeating the same sentence patterns and reviewing them
eg. 'How are you, ....? - I'm fine, thank you. And you?'
'How's the weather today? - It's cloudy(sunny, fine, rainy, stormy..).'
'What time is it now? - It's ten past eight.' etc....
I think...you'll need some assistance from your Japanese colleagues.
I suggest you use some Japanese in your class. (Well...you don't have to actually speak Japanese.)
Let me try to give you an example.
First, you prepare an 'English sheet' like this.
Introduce yourself! ( JAPANESE TRANSLATION )
Hello, my name is........................( JAPANESE TRANSLATION )
I live in ............................( JAPANESE TRANSLATION )
I go to .....................elementary school.( JAPANESE TRANSLATION )
My homeroom teacher is Mr./Ms........( JAPANESE TRANSLATION )
I love/hate him/her very much.( JAPANESE TRANSLATION )
I like tennis/soccer/volleyball/video games...( JAPANESE TRANSLATION )
Thank you.( JAPANESE TRANSLATION )
Second, you ask your Japanese colleagues
1.to translate English into Japanese and write it in the brackets.
2.to write 'katakana' below each English word (to show how to pronounce it...Well...'katakana' does not show correct English pronunciation, but...it's helpful. It's your job to correct their pronunciation.)
Third, you photocopy the sheet and give it to your kids for homework.
You could probably say... 'Next week we're going to use this sheet. I'd like each of you to introduce yourself in English with the sheet. Please fill in the blanks and prepare for the self-introduction next week....etc'
Your kids will try to get more involved in your class as there's something they can understand there - Japanese. Naturally their parents will be much happier.(Well, don't worry too much. They ARE happy now. I think they know you've been trying hard.)
Please try this if you're interested.
And I'm really sorry for my poor English.