It's easier to be a "constitutional lawyer" then I thought. Here's what freshman Senator Mike Lee of Utah had to say about federal laws regarding child labor:
Congress decided it wanted to prohibit [child labor], so it passed a law--no more child labor. The Supreme Court heard a challenge to that and the Supreme Court decided a case in 1918 called Hammer v. Dagenhardt. In that case, the Supreme Court acknowledged something very interesting -- that, as reprehensible as child labor is, and as much as it ought to be abandoned -- that's something that has to be done by state legislators, not by Members of Congress. [...]
This may sound harsh, but it was designed to be that way. It was designed to be a little bit harsh. Not because we like harshness for the sake of harshness, but because we like a clean division of power, so that everybody understands whose job it is to regulate what.
Now, we got rid of child labor, notwithstanding this case. So the entire world did not implode as a result of that ruling.
A couple of problems with Lee's "scholarship":
1) The law overturned in Hammer v. Dagenhart did not state "no more child labor" but rather "prohibited the interstate shipment of goods produced by child labor." That's what's called "commerce" which Congress is expressly given the power to regulate;
2) Lee seems to suggest that despite Hammer v. Dagenhart state legislators "got rid of child labor". This is completely inaccurate. Child labor remained common in the US until the Great Depression when the paucity of adult jobs forced workers to accept wage rates previously paid to children. Even at that, child labor remained legal in the US until;
3) Congress passed the Fair Labor Standards Act in 1938 among other regulations it abolished child labor. Predictably a business challenged the case in court citing Hammer v. Dagenhart and this case, US v. Darby reached the US Supreme Court in 1941. The Court unanimously upheld the FLSA and specifically overruled Hammer v. Dagenhart.
So Senator Lee the idea that Congress can't ban child labor is no longer valid and hasn't been valid for almost 70 years. You are citing a case that is no longer good law and is recognized as an aberration. And while "the entire world didn't implode because of the ruling", it is simply false to assert that child labor was ended without a change in Supreme Court jurisprudence.
These facts are known to anyone who received a C or better in a undergrad Constitutional Law class. That someone who is supposedly a "constitutional lawyer" would make such blatantly incorrect assertions is mind boggling to me.