The easiest introduction to movie making for children is to use Optical toys. I normally start with rollers and flip books then move on to Zoetropes and Thaumatropes. The main thing with children is keeping them busy with projects they can do quickly and get results.
If you are not familiar with Optical Toys then good starting places are:
A recent discovery of some mechanical parts from an unknown Ancient Greek machine has suggested they had some form of mechanical calculator. I have often wondered if they also started animation.
I have never seen any reference to it but Greek vases with figures on them in stages of a walk cycle animate perfectly; and movies have been made of this.
Bearing in mind that these vases are made on a potters wheel, it would not take much imagination to have a 'gate' operated by the wheel so that you saw the figure animate as with a Zoetrope.
One of the problems I had in running workshops in schools is that the Head Teachers would often wonder where 'Animation' fitted in. Some think of it as Art; some as Computer training, and some used it as 'end of week' leisure activity.
It is this 'identity problem' that is perhaps the biggest barrier to getting animation into schools as a core subject; Optical toys are a foot in the door.
Look at Optical Toys