First and foremost I would say that children need to read good poetry -
yes, lots of it. Poetry is an art form, so as with other art forms, you need then to learn a bit about it yourself, for who could play a waltz without knowing what a waltz is, or without knowing how to read music? Who could dance a tarantelle or mazourka without any instruction?
I can recommend Stephen Fry's "The Ode Less Travelled" book to you. He really does explain very simply the preliminaries of writing good poetry, and step by step with him, you will do some exercises to link to what you have learned. If you are a teacher, it will be very simple to follow, chapter by chapter, and I would certainly recommend that your children just get practice writing poetic lines, even if only a couple per day. You could give them a "poetry exercise book" which, perhaps when you are doing the register etc, they could do a couple of lines. This is equivalent to learning the various keys on the piano by practising scales, and without learning this, they are simply writing sentences and nothing else.
If you are teaching children about iambic rhythm, then you will find plenty of my poems written with this rhythm and children could, perhaps, use one of them as a template for their sentences, and here is a simple example:
I am assuming that the children will understand exactly what iambic rhythm is, and that they will have clapped to the strong beat, and also will have thoroughly understood "rhyming". I am assuming that they will understand that in English poetry there are usually either four iambic feet per line which rhyme with the next line, or that there are seven iambic feet spread over two lines, and that lines b and d rhyme? If so, then do this:
I HAVE a FRIEND whose NAME is BILly
Now you try some, using the above as a template for your poem:
eg: I HAVE a CAT whose NAME is MOLly
I HAVE a DOG whose NAME is GEMMa
I HAVE a FROG whose NAME is JUMPy
And they can enjoy themselves making up funny names. They will begin to see that poetry is fun.
In fact, strictly speaking, the last word SHOULD end on a heavy beat, eg: ti TUM ti TUM ti TUM - but at this stage it is not important, and you cannot throw away English words that end on a soft beat. No, if you read your Stephen Fry, you will see that they are called "feminine endings" and are quite acceptable. But let them try some iambic feet next week with "masculine endings".
My FATHer HAS a MOTor CAR
My BROTHer's BOOTS are SMART and CLEAN
My MOTHer BRUSHED my HAIR toDAY etc
I would introduce children to "Rhymezone" or one of the other online rhyming dictionaries. Give them about five words for homework and get them to look them up on Rhymezone and write down some rhyming words. Then the next week they can write their sentences using the rhyming words.
eg: My father has a motor car
Which TAKES us JOURneys NEAR and FAR
My brother's boots are smart and clean -
The CLEANest BOOTS you've EVer SEEN
These are only simple, and possibly silly sentences, but it is getting children to learn how poetry is written and how they can write it also.
If you are not an expert yourself, well tell yourself that I wasn't either when I started to write my first poem for the children in my local school almost six years ago, but I thought that it was worth learning how to do it well, and if I can do it, you can also. As you progress through your book, doing your exercises, I will be aware of the fact that there will be some experts following me and competition also, for writing poetry is really addictive, especially when you have a keen audience awaiting your next poem. My keen audience not only awaited the next poem, but often brought me the subject for the poem also, ha ha. I think many teachers will find it quite fun teaching their children to write poetry, but don't expect to ask a poet to come to your classroom and teach them everything that is in Stephen Fry's book in one lesson and to leave the classroom with the children having written a full blown poem themselves. It would be like asking a musician to teach a child to write a waltz for the piano in one lesson. Yes, someone can teach children to write prose broken down into small lines, and lead them to believe it is a poem, but most children will know that this isn't the case. Teach them properly is my advice, and teach them over time, with regular practice, as with any art.