http://www.dol.gov/elaws/esa/flsa/cl/exemptions.asp
The Fair Labor Standards Act provides for certain exemptions. Youth younger than 16 years of age working in nonagricultural employment in a business solely owned by their parents or by persons standing in place of their parents, may work any time of day and for any number of hours. However, parents are prohibited from employing their child in manufacturing or mining or in any of the occupations declared hazardous by the Secretary of Labor.
In addition, the child labor rules do not apply to:
Youth employed as actors or performers in motion pictures, theatrical, radio, or television productions;
Youth engaged in the delivery of newspapers to consumers; and
Youth working at home in the making of wreaths composed of natural holly, pine, cedar, or other evergreens (including the harvesting of the evergreens).
Agriculture is a separate exemption.
Youth of any age may be employed at any time, in any occupation in agriculture on a farm owned or operated by their parent or person standing in place of their parent.
Edit: Above response moot per OP's comment.
http://www.dol.gov/whd/regs/compliance/whdfs58.pdf
https://www.law.cornell.edu/uscode/text/29/212
Violation is a federal misdemeanor, with up to 6 months in prison upon a
second offense.
http://www.mass.gov/lwd/labor-standards/dls/youth-employment/summary-of-massachusetts-laws-regulating.html
https://malegislature.gov/Laws/GeneralLaws/PartI/TitleXXI/Chapter149
Sections 60 to 78 of the above link are relevant.
https://malegislature.gov/Laws/GeneralLaws/PartI/TitleXXI/Chapter149/Section78
Under MA state law, the penalty is a fine of $500-5000 and up to one month in prison, with each day being a separate offense.
MA law appears to be stricter than federal as relates to family businesses.