Child actors are hired to play children in film, television, commercials and stage. The best time to start acting is when you are a child. This is because the entertainment industry is always looking for the next child star. There are always more acting roles for kids than there are for adults. 

If you are a parent looking to get your kids into acting it would best to get your child into acting classes. Talent agents and casting directors love kids that have outgoing personalities, a great look and have a life outside of their acting interests  such as extracurricular activities. Having a maturity beyond their years will also be necessary. This can help with the audition process and when your child gets on the set. 

The only way to score legitimate work for your child and get acting parts is to get a talent agent.