No, child actors should not be required to invest a certain percentage of their earnings. It is not just for the government to tell anyone what they should do with their money, even if that person is a child. In ideal circumstances, a child's parents would help him or her manage the money wisely.
Child actors are paid a large income at an early age and need to have responsible financial guidance. There should not be a requirement to invest a percentage of their earnings but instead a requirement to save a fixed amount in an insured non-risky account. That will allow them to have some financial stability in their later years.
Child actors should not be required to invest a portion of their earnings. No one should be required to invest their earnings, and investment should be a completely voluntary act. However, as child actors' money is controlled by their parents, I would personally urge the parents to invest the child's money to secure their future, but by no means should it be mandatory.
Child actors should not be required to invest a certain percentage of their earnings. Although child actors need certain protections due to their age, requiring a certain amount of investment is too restrictive. It can be a hardship for certain families that need the money. Forcing investments may also cause people to make bad decisions with money.