It's my opinion that you are never doing a child a favor by letting him be rude or train half heartedly.
At our dojo, aikido training is spoken of as a privilege and never a right. Bookman sensei asks kids regularly both privately and in front of others why they want to do aikido, or if they want to. Discipline is always maintained.Part of the training is about self respect and respect of others.I think kids crave the formal structure of the dojo and like all the bowing and thanking people. The ones that take adult class are always on best behavior. Sensei calls them up to Uke and they love it!
Good luck with the little darlings. Just define your goals and stick to them. The kids'll come around.