I started my grandchildren younger than that.
They did a pillow case, then pajamas. These items were selected because they could use them with pride, and if seams were not just perfect,no matter. The pajams were pull on pants and over the head top, simular to medical scrubs.
I agree with previous posts that to do "real" sewing, you need a "real" machine, not a toy. A 10 year old can handle that.