My sister that's a barber told me, when possible just let kids hair grow out until they are old enough to express how they feel
Her worst experiences have been cutting children's hair for the first time
My barber has a rule that he doesn't cut any kid under the age of 4. One he said their hairline ain't fully there yet and parents fuck their kids up giving them cuts too early. And the 2nd is because by 4 the kids are more than likely able to sit still and understand the actual experience isn't scary.