Dear Mandy
Yes I agree with Martyboy's post that there is no point reinventing the wheel - get a good textbook as your guide so that you teach the most common vocab themes and build up in a logical way.
However most publishers of textbooks like to sell a lot of books so they don't just have a book for teacher, they also have a textbook, a workbook, a fun book and so on - they want the schools to buy ALL of them, one copy per child and that makes for a lot of books!
The good news is that just with the textbook as your base you can follow the curriculum laid out there and use anything in it that you like, but mostly you teach that curriculum using language games.
Language games will drill and practise any skill: listening, speaking, reading and writing.
You can get some free samples from my book 161 English Language Games for children from my site.
As you have wide age ranges in your groups concentrate on the better half of the class so that they don't go mad with boredom.. I mean a ten year old learns at a much quicker pace than a five year old and if you wait till all the five year olds have got it the ten year olds will have torn their hair out.
Kind regards
Shelley
PS Here is the page where you can receive the free games - there is plenty of guidance about how to use them and they can be adapted to teach anything:
Get
free games from my contact page.
ESL games and activities for teaching English to children