In Uncanny X-Men Annual #12, the X-Men are assumed to be dead (having died in Dallas, only to be resurrected by the goddess Roma). Mojo, missing his greatest rating generators, had his people try to recreate his own version of the X-Men. After many unsuccessful attempts, the X-Babies were created. They soon rebel against Mojo. Mojo was about to kill them when he was told that their instant ratings were the highest ever recorded.
There have been several incarnations of the X-Babies over the years, usually resembling whatever the current team of X-Men is. There has also been a similar team instead based on the Avengers, called the Mitey 'Vengers, who appeared in the X-Babies Reborn one-shot. There have also been several X-Babies villain teams including the "Brotherhood of Bullies" based on the Brotherhood of Mutants (X-Babies Murderama, 1998).
In Excalibur: Mojo Mayhem (1989), Kitty Pryde, interrupted on a train trip, helps a team of X-Babies flee from a Mojo enforcer who is intent on getting them back by tricking them into signing contracts. In this incarnation, the children's child-like faults and crushes on each other are cruelly exploited by their adversary. Kitty, with backup, ends up saving the day.
Several incarnations of the X-Babies are friendly with Ricochet Rita, the good past-self of the villain Spiral. Due to Spiral's time travel abilities, Rita, the babies and Spiral can all exist at the same period simultaneously.
In Exiles #8, it is shown that the reality-hopping Exiles encountered a version of the X-Babies. It is not stated whether these X-Babies are the creation of Mojo or the X-Men of the reality in question. In fact, no further details are given except for the narrative commentary "The less said about this, the better."
The X-Men were once again reduced to infancy by Mojo during Uncanny X-Men #461 (2005). As kids, they were able to defeat the villains and restore their rightful ages, though Juggernaut had second thoughts.