I love to teach kids but it is certainly different from adults in some (not all) ways. To begin with, they do not have any English experience. Next, they have shallower experience levels than adults. But they also are more inclined to try to guess what you want them to do. You will find using pictures really helpful this way.
You can start with the straightforward and simple ‘I have…’ saying it as you pick something up, or take it out of another thing (like a bag). Repeat this a few times, and then gesture for them to take (get) something, and to try repeating the sentence. 9 times out of 10 they will get it right.
The problem is that they may not see the difference between ‘I have…’ and ‘It is…’.
What can we do?
Start to use ‘It is…’ with objects you are not holding. They will see the difference, particularly if you emphasize it and repeat it a bit.
Now, how can we distinguish between ‘I have…’ and ‘I am holding…’ ?
You may wish to draw a picture of your home… keep it simple. a bedroom with a few obvious bedroom type things in it is good. Point to one of the objects (a bed) and say, ‘I have a bed.’ Repeat a few times. then let them draw their houses, and do the same.
Be sure not to get into difficult things that take a lot of explaining. computers are easy to understand. So are beds, tables and to a lesser extent chairs. Chests of drawers are not easy for most children. Ninttendo DS is a great one. and televisions. Stick to these kinds of things and then more to even more sundry (books, bags, socks, cups etc).
As they get more comfortable with this expression, introduce the expression ‘Do you have a…? ‘ You may get a box of objects that they know the names for, and hide it. Have them get something but not show it. Ask ‘do you have a (name of one of the objects)?’ and they reply ‘yes I do/no I don’t’.
Move into more fun stuff after a while… ‘Do you have a pink gorilla?’ or something of that nature and soon they will love to ask each otehr silly questions in English. Bang! Internal motivation!
Have fun teaching!