I learned to sew by hand first, then my mother taught me to the use the machine when I was 8 years old. But she taught me so I could sew my Barbie clothes. Why not ask the girls what they want to make and then go from there. If you find out the goal is to make clothes then let them know that will take time and they need to start with the basics. If you have a pattern to show them why it takes time. If you get too detailed or pick things they care nothing about then they will be bored and lose interest. Even in HomeEc we chose our own pattern.
Have fun!