I'm Not Complaining...
In all the campaigns in which I have played a halfling, never has anyone-NPC or PC- attepmted to disable a halfling in the logical way. Sitting on them.
Since halflings are the size class of small, all other basic character races (other than gnomes) are one or more size class bigger than them. Meaning that a halfling character will always have disadvantage against grappling (unless they've taken the grappler's feat).
Once the halfling has been successfully grappled, all they have to do is sit on them and watch as they start making strength saving throws with disadvantage because they're beginning to sufficate under the weight of a creature one or more size classes larger. Each couple or so of failed saving throws result in gaining levels of exhaustion. They reach a high enough level of exhaustion and pass out.
Of course, there is the issue of practialy being prone during this, since you wouldn't be able to move from sitting on them. But in that situation, you could always threaten the rest of the group with the death of the halfling companion. Grappling someone can indeed result in hostages.
