I saw this winter-plumaged Little Stint on Saturday. The bird was associating with Red-necked Stints just outside the hide, allowing good comparison between the species. Although the plumage difference was not obvious, the structural differences were apparent, including:
Slightly larger body size of Little Stint
Longer legs (especially above knee)
Longer, finer bill tapering towards tip
Less horizontal posture
Slightly longer neck, making head seem to sit more on top of the body.
The behaviour was also different, Little Stint seeming to pick at the surface of the mud (rather than the shuffling, probing action of Red-necked)
Most of these structural differences can be seen in the last (excellent!) photo posted by Cherry.
I am not sure about the additional photo posted - it may be Little Stint (some of the structural features seem to fit) but the angle is not very clear.