All halflings have the Halfling Nimbleness feature:
You can move through the space of any creature that is of a size larger than yours.
Lightfoot Halflings have the Naturally Stealthy ability:
You can attempt to hide even when you are obscured only by a creature that is at least one size larger than you.
Halflings are sized small, while Dragonborn, for instance, are medium.
A rogue has a Cunning Action:
You can take a bonus action on each of your turns in combat. This action can be used only to take the Dash, Disengage, or Hide action.
And our group has been playing with a Barbarian Dragonborn and the Lightfoot Halfling Rogue. In combat, let's say, facing a single boss, the rogue usually hits and hides behind the Dragonborn (moving through him). A stealth check is rolled against the boss's perception, and if the boss wins, he can go around the barbarian and hit the rogue. He does not trigger attacks of opportunity because he is not leaving the barbarian's melee range.
However, for the rogue to go behind the dragonborn, he should trigger an opportunity attack from the boss, right? Or can the hide action include this 5 feet move to hide behind the dragonborn? Or does the nimbleness feature prevent attacks of opportunity, since the rogue can simply stand in the dragonborn's space, only behind him? Does standing in the same space as a bigger creature prevent attacks against you because the creature shields you?
In terms of RP and realism, we've been describing this as such: the halfling is hiding in the back of the barbarian, pops out to strike, and hides back there. The idea here is to have the rogue safely out of harm's way (dumb enemies won't understand where he is, others will attack with disadvantage, and others will actually have to move to him him (unless they're grappled).