Here is what the traveling with children section says on their website.
Infants under two years of age throughout the duration of their vacation may fly and stay free, but must sit on an adultâ€™s lap and do not receive a separate baggage allowance. Some scheduled airlines may charge for infants, including air-related taxes, and some countries do charge infant departure taxes. Any such charges by independent suppliers or governments are the responsibility of the client. Restrictions may apply to â€œKids Stay, Play and Eat FREEâ€ programs and most hotels require that children must be accompanied by full-paying adults and pay airfare. Policies vary by individual hotels. Hotels may check the passports of children at check-in to verify they qualify for any discounted child room rate.
At select hotels in Cancun and Riviera Maya, a single parent traveling with up to two or three children (varies by hotel) is not charged the single supplement. The hotels reserve the right to collect the single supplement in resort, or cancel any extra room upon arrival, if the promotional policy is not used in the manner for which it was intended. Restrictions apply.