Yes. Americans visiting Cancún as tourists must pay VISITAX, a mandatory visitor tax charged by the state of Quintana Roo. It applies to foreign tourists, including children. visitax.gob.mx

• When: Pay before leaving Quintana Roo; you can pay in advance.
• Separate charge: It is separate from airfare and hotel or environmental taxes. Save the QR-code receipt after payment. visitax.app
• Where: Use the official government VISITAX website, which will show the applicable amount during payment. visitax.gob.mx

It’s a state tourist tax associated with your visit, rather than a payment you necessarily have to make at immigration upon arrival.