I encourage my children to say "Yes". I always correct them when they say "yeah" or "Yep" which they have been learning at childcare off the other children. It sounds low brow and un-educated. I am not going to let my children lose a potential scholarship, job interview or a potential partner due to incorrect language (I am a stickler for manners too).
I also correct me, myself and I; you and ewes; and any number of american words which they feel the need to try to say like cupcakes and cookies.
It is my job as a parent to teach my example and I do.
My children are only 2 and 4. It is never too early.
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I love diggin' in the dirt
With just a pick and brush
Finding fossils is my aim
So I'm never in a rush