How young did some children begin to work during the Industrial Revolution?

Four years old.

In specific, the Industrial Revolution affected the lives of working class people and the children of industrial societies. Child labor was a common sight in industrial societies as children as young as four years old were often employed in the factories and industrial complexes that developed during the time.

the answer is: must pay taxes on profits

since it is considered as a part of your income, profits from investments is eligible for tax payment.

the tax from your investment could be influenced by how long you decided to sell it. united states promotes keeping your investment for long term period. so, the tax rate for investments that you sell in less than one year is typically higher compared to investments that you sell in more than one year period.