Army Men Wiki

The Mini-Soldier is an NPC encountered only in Army Men: Sarge's Heroes 2. They are miniaturized versions of regular army men, and come in both Tan and Green. Though only around a third of the height of a regular soldier, but wield a regular-sized gun.

Mini-Tan Soldiers show up only in the levels Cashier, Train, Pool Table, and Pinball Table. The mission Train in particular takes place in a town that seems to be scaled to the size of the mini-soldiers, and a Mini-Green Soldier briefly shows up here at the beginning of the mission before being blown up.

While it's not made explicit where the Mini-Soldiers came from, it seems to be implied that they were toys found in the mini-town in the Toy Store by General Plastro, who then sprayed them with the Plastrification Cure Serum.