There are some really good haiku examples out there for kids if you have a look online and in your local library.
Luckily poetry for children has become more accepted by mainstream poets. At one point it was looked down on and that's a shame because people who are good with words can create wonderful haiku for children.
I especially like the ones which tell a joke or a riddle. If you can get the kids involved with the poetry, they'll always enjoy it.
When I was a kid this was my favorite kind of poetry. It just seemed so easy and fun to go around composing little snippets of my day into a three line form.
And last year I managed to get a haiku of mine published. So I guess it's a good idea to start them off young!