I've come up with several answers, hopefully this helps and isn't too confusing!
1836 First state child labor law Massachusetts requires children under 15 working in factories to attend school at least 3 months/year
1842 States begin limiting children's work days
1938 Federal regulation of child labor achieved in Fair Labor Standards Act
Congress passed the first child labor laws in 1937
The FLSA outlawed most child labor in 1935, the depths of the Depression, to eliminate kids competing with adults for the few jobs available.