My granddaughters and the preschool kids I used to volunteer with were all sewing at 4 yrs old. We did use a brother machine set on turtle speed. I did not stress things like 1/4” seam or accuracy- some seems were 1” wide at one end & 2 at the other- it was all ok- we made it work and they loved it- were always proud of their accomplishments and their parents loved their creations too. The technical stuff comes along as they continue just like all of us, we improve with practice. I had boys who sewed the blocks on our fundraiser class quilt when they were 4 and then came back to me when 8 or 9 wanting to make pants, vests, hunting/ fishing vests, gifts for their moms or grandmas.
encouraging and praising what ever they make keeps them interested for years to come. If you start out expecting perfection they lose interest pretty quickly