There have been multiple legislative proposals enacted in order to specifically protect children.
Children's Online Protection Act (attempted to make illegal commercial website content that is offensive to minors - status: unconstitutional but litigation is pending)
Children's Internet Protection Act (conditions receipt of ERate funding from the FCC by schools and libraries on creation of an Internet Safety Plan that includes filters)
Communications Decency Act (attempted to criminalize indecent content on the Internet - unconstitutional)
Sec. 703: Misleading Words or Digital Images on the Internet (amending 18 USC § 2252C to make it illegal to embed "words or digital images into the source code of a website with the intent to deceive a person into viewing material constituting obscenity")