I will introduce my child ti trading when he at least 18 year old. Before 18 year he should be busy in getting education. After 18 year usually a child become mature and he can seek basic of trading easily.
The minimum age of 18 years is quite reasonable to introduce any child to trading at least that child would have mature enough at that age thus psychologically and mentally balanced.
Rushing a child age 10 to trading might be counterproductive in the sense that it can jeopardize their educational system, they might not be able to cope with the rigorous skills required for trading at that tender age, obviously any age above 18 is my desire age limit for introducing my child to trading after completing their high school and college.