I would second Emile's advice. I teach (Korean age) 6 & 7 yr olds and while I wouldn't call a lesson "a grammar lesson", I teach them verb subject agreement, adjective placement, comparative & even superlative adjectives etc. when it comes up.
I think it will come naturally in the course of the lessons so when it is right to include "I am, you are " eg they can grasp the concept easily enough.
There are a heap of great websites out there for kids. This one and
www.mes-english.com, bogglesworldesl.com abcteach.com eslkidstuff.com
Try and find, if you haven't already, a good bookshop to see what ESL textbooks there are. I use Magic Time with one of my classes and while some of it is still a little difficult it is well structured so you can get ideas from it at the least.
ONe tip, for what it's worth, is just persevere..! Kids will talk about anything so the trick is to get them to "accept you". Once they are comfortable around you they will want to share stories and ideas and that is where the language will come from. They are have notoriously short attention spans so don't despair if a worksheet that you have spent an hour on is dismissed by them in 5 minutes. Arm yourself with a number of activities, worksheets, songs, games and just chop and change as it's needed. Remember the successful ones as you can re-use, re-cycle, re-work. Kids don't mind that.
Good luck, if you need any more info, just shout!
xx jen