According to the tour guide I overheard at Chichen Itza, it was an honor bestowed on certain families to have their babies chosen for sacrifice. The babies were brought up in the knowledge that they would be sacrificed for the greater good of the tribe and their sacrificial ceremony when they reached the proper age (12?)was much like a wedding celebration. I have not been able to verify this.
http://www.jaguar-sun.com/maya.html
There were many forms of human sacrifice and some were captured enemy warriors. The truth is that no one really knows. I also heard the tour guide tell the tourists that the team that lost the match in the Mayan ballgame would be sacrificed. I can imagine that perhaps this happened at the end of a cycle, but not on a regular basis.
http://www.jaguar-sun.com/ballgame.html
There were about 159 hits on google when I searched "Mayan sacrifices cenotes". I will look into this further, later on.

Edit: Tour guides at the Mayan ruins suffer no compunctions about offering lurid details as facts, either. The tourists want to be titilated by "heathen worship practices", the gorier the better. The tour guides have found that the tips are better if they tell great yarns. Human nature, after all.