Kid Quantum is the name of three superheroes appearing in comic books published by DC Comics, primarily as members of the Legion of Super-Heroes.

James Cullen, the first Kid Quantum, was retconned into the Legion's past, ostensibly as a result of a history-changing disaster. He is described as having been the first Legionnaire to die in action after the belt that he derives his powers from malfunctioned. Following Cullen's death, a rule was implemented that forbid Legionnaires who derived their powers from technology. It is later revealed that Cullen is a humanoid body used by the Proteans, a shapeshifting alien species, to protect them from the villain Glorith. Rather than being killed, Cullen had gone into hiding.

The post-Zero Hour incarnation of James Cullen shares a similar history to his original counterpart. Unlike his previous counterpart, Cullen is definitively established to have died.

The second Kid Quantum is James' sister Jazmin Cullen, who underwent surgery to augment her power and no longer have to use the belt. Despite initial hostility from the Legion's members, she is eventually elected leader of the team and later enters a relationship with Cosmic Boy.

In the miniseries Countdown: Arena, an alternate universe variant of James Cullen / Kid Quantum appears as a counterpart of Monarch. In the final issue of the series, Monarch kills Kid Quantum and his alternate universe counterparts to gain their powers.

Both incarnations of Kid Quantum possess the ability to create time-stasis fields in a limited area, within which they can slow down or accelerate time. The fields are usually no larger than a person, and the effect is measured in minutes rather than something long term.