I've taught beginners of all ages. For children remember to plan a simple project with a great appeal and immediate results. Hand sewing isn't going to meet this goal for most children. The best project I've found are the popular "hot dog/burrito" pillowcases to get them "hooked" with instant gratification. There are youtube videos- something they are familiar with. Working with a pre-cut kit I've had even 6 year olds thrilled with their completed project (Spiderman, Little Mermaid, etc fabrics). Depending on their age it might be simplest to have them sew one using a seam guide and an adult helper. At another session start to discuss threading the machine, measuring, seam allowances, etc. They can practice sewing along the lines on a piece of paper. It's wonderful to get them sewing at a young age!