The thing about kids, and I believe everyone that has been around them would tell you this, is that they have short attention spans.
Keeping that in mind, when one is trying to teach kids aikido, one must hold their attention by doing fun techniques. Mix up the forms of the techniques you are by practicing variations and give them games to do (I also like to let the kids try and catch me in a form of randori) that they would like. Try shikko soccer (I'm going to pass that on to sensei and see if we can do it
) and stuff like that. Just remember, have fun.