I dislike the idea of paying to learn how to handle a bicycle in situations, but some sort of education is greatly needed for children in order for them to operate a bicycle in traffic situations safely.
Being a father too, I would definately use every option to my advantage.
I'd definately try some sort of "what would you do if..." type of training with the older child. The younger one could prove to be more difficult given age and lack of experiences along with a lesser understanding of how things work. Maybe try and instill in the older child that the younger one looks to her for example. That way the older child might think twice before making decisions when you are in group rides.
I guess this is one area where I can somewhat agree with Helmet Head. If you have the money then the training for the children can't hurt, it can only be an advantage.