I have used the children sewing machines with children aged7-8 but it was too slow.
I did allow my young nephew at 4/5 use my brother sewing machine to sew on. I had just purchased the machine and he had stood very quietly and listened to all the information. Because it has a speed control I set at slow,.he also used to sew his quilt . Although I did most he did have ago. And sewing in the ditch.