First of all I would suggest you use light balls so they don't hurt their feet.   Try lining two balls together and touching......ask them to kick through the first ball trying to kick the second ball. This gets them to kick through the ball. 

Another thought on youngsters learning to strike a ball ..........if you can use a panelled ball place a panel against the laces of the child's boot; this gets them to feel to contact areas and hopefully avoid using  the toe.       Or/and if they run straight onto a stationary ball   the leg swing is restricted and hence the use of the toe. If you can get them to approach the ball from a small distance to the left or right depending on which foot they prefer.....swing through a little like a golf swing. ' the rugby approach to striking the ball going for a conversion.

Try it and see

hi micheal

you could simply just try close half and full volleys this would get them used to the feeling of using the top of their foot then you could move onto short side volleys and also kicking a ball off a cone.

pratice these movements alot and the girls will get used to the actions and feelings untill they become more natural.

most of the time the "feel" can be more important than the technique