Size Diff, every day.

It keeps the doctor away

The billhook looks great and It makes sense that smol critters would favor polearms, cool world details

indeed. if you are smaller, you need a weapon that is a "big" equalizer.

another great option would be poison arrows or darts. But that's not a weapon particularly well suited for guard duty - so those, if they exist, might only be taken out for 'special occasions'

fire is another great equalizer. i figure those wicker weave skills might be well suited to craft containers that hold flammable substances such as tar or more violent combustables, which could be slung around on a rope or chain to use both in melee as a medium distance weapon or even as a throwing projectile. Also great against any cavallery if such exists.

imagine a little tightly woven basket of around 1-2 pound weight, filled with wax, tar, fat or any combination of such, maybe with a bit of saltpeter or metal powders or any such alchemy added for good measure, knotted to a chain about 3 yards long. The wicker will act as a "wig" - making sure the fire burns steady and for a long time without consuming itself - and without going out when the thing is slung around. You can smash it in peoples faces, set their cloth on fire, make the flaming chain wrap around opponents limbs and torsos to trap and burn them in the same stroke.

again something that would only come out in special occasions, and probably not too close to the village - or the wicker fields - for obvious reasons.

Those flame weapons would be obscenely expensive to use, and more of a danger to the user than necessary.

So are nukes.

More closely related, so was "greek fire" (in 800 AD) or "fire ships" (1700 AD)

There's some merit to weapons that you have in order to convince your attacker to not attack, even if you really don't want to use them. Or if you use them end the battle decisively - even though costly.

But I was thinking hard about the practicality. The chains would be expensive to make, but reusable. The tar filled balls that go at the end are ammunition, they are single use, once lit they would stay lit until they burn out - at which point they are a smoldering husk. You could probably carry a backpack full of them with you, and each one would burn for 5-20 minutes depending on composition, enough to last the whole fight.
They would be a very costly weapon, but in comparison not an unreasonably costly one for a "high stakes" situation.

Self-protection is a crucial aspect (just as with the examples above) and it would be a risky affair, but there are mitigations. The most important one would be to make sure the burning oily residue does not stick to fur and clothing, and whatever they wear or cover themselves which is very hard to set on fire. The trick there might be that tar, wax and fat really does not want to burn unless it gets really hot. In the basket that is achieved by means of having a wig that allows the material to melt, and then soak into a fabric with high surface area from which it can evaporate and burn continuously. Like a candle or a torch.

Ironically, covering themselves with flammable sticky stuff with a much higher melting point that completely covers any fur or cloth would not catch fire if in contact with the flaming ball. it would melt a bit on the surface and the melted stuff would stick to the ball - and burn on the ball, but no flame would stay behind when the ball is taken away. That would also protect and cool whatever is underneath. So you could touch the flaming ball briefly (if hit by accident) without catching fire.

Continuous exposure is a different thing. They would burn like torches (for example if a mouse flame warrior fell, and the flaming ball would stay on him for half a minute or longer) . But that could be used in psychological warfare. Assume the mice attacking a fortress or town, a fallen mouse might be a larger fire hazard than a living one. --- A property completely unsuited for town defense though.

Considering materials of the era, I would suggest a double layered fire-rpotective clothing. The inner layer would be cloth soaked in water. The outer layer would be cloth covered thickly in tar or a waxy substance (with high melt point) - If - worst case - the outer layer did catch fire, it could be discarded while running away

Last but not least, considering the reproductive strategy of mice, "glorious suicide warriors" would be a viable tactic. But in most military settings, what matters is less the loss of life, but the cost of replacement of the fallen soldier by means of necessary time for training and equipment. The fire-ball wielders would need significant skill, their role would not be a suicide "burning mouse berserker" - but more that of a "fire wizard" - lets not forget, against a suitable high stake target the balls can be released from their chains and flung at the target, like stones from a sling - literally "fireballs"

I love all those little guys hiding around <3

You'd come out to gawk too if someone three times your size visited town.