What if your boss doesn't let you take your child to work with you on take your child to work day?

This depends entirely on the nature of where you work and whether your employer would permit it. There aren't any laws that directly address it (there are laws that might generally prohibit minors in a particular type of business, i.e. bars). If you work in a steel mill, nuclear power plant, or a gentleman's club, I would think it would not be very practical to bring a child to work. On the other hand, if you work in a child care facility, and your employer agrees, it probably doesn't present much of a problem.