The Lion Habitat at MGM Grand opened on July 1, 1999, a collaboration between the company known for its Leo the Lion mascot and big-cat trainer and conservationist Keith Evans. The aim of the Habitat is to both raise public awareness about the issues facing lions in the wild (poaching, loss of habitat, disease, etc.) and to aid in the lions' socialization process, making them easier to tame and train.
The lions don't live at the MGM, but rather at Evan's 8 1/2-acre compound, from which different groups from the total of around 40 big cats (including lions, tigers, and a snow leopard) owned by Evans and his wife are transported each day to the Strip. And you're correct: When cubs reach an age to be socialized without being too big for young kids to handle, photo opportunities are available. The Habitat is free to visit, but photos start at $25 and up.
Right now, no cubs are available for photographs as the last two that were, named Dude and Marina, have been too big for children to handle since last spring, although they're in the rotation for visits to the Habitat. The good news is that some new cubs are scheduled to begin the human-interaction process and should be ready for pictures in week or so. As soon as they are, it'll be posted on Keith Evans' site, so tune in regularly to www.lionpics.us for updates.