I'm my sci-fi setting's history, various hominid species are in competition with each other for dominance of earth and its resources. Among these races are "Halflings" ... okay, not haflings per se, but rather like Homo florensis with an upgrade, namely human level intelligence (or H. Sapiens with an advanced case of insular dwarfism). The primary trait of these "Halflings" is a very small stature, standing but 0.9 - 1.1 meters tall. Now, this is small, very small, though it may give them some advantages (for example they would be but ~33% the mass of humans and thus they could have thrice the population density in the same amount of land).
There is a long and attested history of anthropologically smaller peoples being dominated by larger ones. Since they are so small, I see no reason why man i. e. homo sapiens (and in this world, his fellows) would not immediately steamroll over any population of halflings they encounter. So I have opted to include some unique biological quirks that might give them the edge over H. sapiens. At present, they have at least the following traits:
a height of 90 ~ 110 cm (the stature [and possibly strength] of a 5 year old)
a physical maturity age of 9 ~ 10 (though a mental maturity age in the mid teens)
the intelligence of an average human
(at minimum) average human lifespan
Ideally these Halfling become a problem and serious rival to humanity in the future, but I don't see a group race of homonids the size of 5 year olds standing a chance against any human population, much less seriously challenging them. So, sticking to that which is in the realm of evolutionary possibility (700,000 ish years of evolution).
What biological traits could I realistically endow the Halflings with to give them at least a fighting change against humans?