My DGS is a little older (8) but when he was 7, I started teaching him how to sew. I started with simple basics of how the machine works...AND TO KEEP FINGERS AWAY FROM NEEDLE... He picked it up quickly. This week when he came, we made simple Christmas ornaments which were 2 squares about 4x4. I showed him how to put right sides together to stitch and he pinned it, then stitched it. He turned it right side out, then he stuffed it with fiberfill and then we pinned (together) the opening and stitched it. He was SO PROUD!!
Some say to let them stitch on paper with you pressing the foot pedal to get them used to sewing a straight seam. My 5yo DGD took to that very quickly. I show both of them the 1/4" and used a post it note taped with masking tape for them to use as a guide.
Do I dare say they can do a better 1/4" seam than I can!! LOL