What a great question. I taught my daughter the basics when she was young? Maybe 8 or so? Then when she was a teenager she made her sleeping PJ pants and shorts from flannel. She did a great job. She knows enough to get by and mend something, but never did really like it. Now she's buying her first house, and on the phone yesterday she said "I think I'll make the curtains."
I've heard that sewing skips everyother generation. If grandma sews, then mom usually doesn't sew much, not feeling as good as grandma, then granddaughter takes it up again. That's true in my family. My grandma sewed, my mother barely gets by, but my sisters and I all sew up a storm.
Most off, if your child has an interest, by all means teach! (notice I said child, because boys and men) sew too! As all of you know, sewing is a great way to spread your imagination. Stitch on! Sara