My 4 y/o niece sews on my treadle machine. She peddles the treadle as best as she can and I help at the top making sure the wheel goes into a rotation. She does really well and up to a good speed. Just make sure little fingers stay out of the way. We have put together blocks but no quilting.
I don't let her use my electric machine as I don't even like sewing on it lol
Its good to teach them young